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Discussion thread for /data EMMC lockup/corruption bug

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sfhub

Senior Member
Oct 23, 2008
5,342
7,219
This post will evolve over time as more info is found:

Latest Updates
6/24 Custom PIT repartition workaround posted by Jaymoon.
You lose 8GB (some of which might be further recoverable with extra work) and restores using the original PIT will lockup your phone again (a scenario that could happen if you brought your phone back to Sprint for some unrelated problem) so if you have the opportunity to get your phone replaced with little to no cost, IMO that should be your primary option.
http://forum.xda-developers.com/showthread.php?p=27852689#post27852689

E4GT specific PIT file here (theoretically instead of losing 8GB, you'll only lose 2GB):
http://forum.xda-developers.com/showpost.php?p=28070569&postcount=654

6/8 Update for other platforms waiting for fix
Codeworkx's contact with Samsung got following response [discussion]
Update 14:56 CEST:
Patches will be out in form of new official ROMs and also sourcecode releases after testing, which might take some time.

6/7 Update
Test plan posted - see bottom of post for results so far (esoteric68, krazy_smokezalot report success)
BIG THANKS to Esoteric68 (and robertm2011 before her) who took the plunge to benefit everyone else. She has completed the test plan and more. 6 flashes of CM9, 3 flashes of AOKP, 3 wipe data/factory resets, and 3 nandroid restores, 1 stock FF02 flash, all successful. We are ready to have more testers try out the test ROM installs. We are getting more confident the code analysis was correct.

6/2 Update
Less technical summary and preparation for new round of testing

5/31 Lots of discussion on the code path detailing how the problem occurs and where to put the workaround, select posts below
Call trace for CWM Recovery - wipe data/factory reset
Call trace for CWM Recovery - restore
Section of update-binary afflicted by same issue as wipe data/factory reset
Recap of where workarounds can be placed
MD5s of various update-binary executables
Pros/Cons of placing workaround in kernel vs libext4_utils.a
Are ICS nandroid backup/restores safe?
Are ICS recoveries safe?
Why do CM9/AOKP installs often brick in ICS but not in GB?

5/24 Update pretty much ties up all the loose ends - Thanks Mr. Sumrall, Garwynn, Entropy, and everyone else who pitched in!
http://forum.xda-developers.com/showthread.php?p=26521643#post26521643

Potentially very GOOD NEWS
It appears Sprint/Samsung tested the EMMC brick issue, confirmed the problem, and tested a fix that appears to resolve the problem:
http://forum.xda-developers.com/showthread.php?p=26465085#post26465085
To clarify this...in testing done over the weekend, there was a small "subtest" group which consisted of 20 devices. This group was put together STRICTLY for the propose of testing the emmc bug and fix. The devices were all programmed with the data known to have cause bricks when wiping. Of those 20, all but 6 also had the code patch to resolve that issue, so there was a possibility for 6 hard bricks, only 4 actually bricked, therefore, on the build currently being tested, the "emmc break issue" has been deemed "resolved"



We now have an update on why this bug is happening and which PRV/fwrevs are affected. PRV/fwrev 0x19 are susceptible to the EMMC /data corruption issue (which should now be referred to as EMMC lockup issue). PRV/fwrev 0x25 has the fix for the lockup issue but has a separate 32KB of zeros data corruption issue, which is being patched in the kernel (our kernels don't have that patch). All these problems are in the EMMC firmware. It can potentially be updated, but nothing is publicly available. EMMC lockup issue is triggered on erasing the EMMC. The only piece we have not been able to explain is why GB-based kernels seem immune to the EMMC lockup problem whereas ICS seems more susceptible to the problem. Presumably both are doing ERASE commands, but possibly in slightly different ways. See these posts for more details [#1 / #2]

To get your PRV/fwrev, you can use this (if you have busybox installed):
[email protected]:/ $ su
[email protected]:/ # cd /sys/class/block/mmcblk0/device

[email protected]:/sys/class/block/mmcblk0/device # cat cid | cut -b 19,20
19
If you don't have busybox installed just visually parse the line, match the serial # (0xd3f24fe6 - example only - yours will be different) with the cid, and look at the 2 numbers before the serial #.
[email protected]:/ $ su
[email protected]:/ # cd /sys/class/block/mmcblk0/device

[email protected]:/sys/class/block/mmcblk0/device # cat serial cid
0xd3f24fe6
1501004d414734464119d3f24fe68e8b

It appears after looking at the code more closely and examining the results of the card info dumps, we do not have this fix in our kernel. It isn't clear whether the fix would resolve our /data EMMC brick issues, but the point is moot right now because we don't have the fix.

Possible BRICK here. Please do NOT do any more testing until further notice. Please do NOT use Wipe Data/Factory Reset. It is the main difference between first and 2nd round of testing and is the current suspect

FE10 repacks added to Resource section

Esoteric68, azyouthinkeyeiz, and robertm2011 are testing flashing different ROMs with FE07/FE10 repacked with unlocked recovery. We all owe them our thanks for risking their phones to help the community (taking one for the team) No bricks so far.

Separately we are still discussing whether the fix Samsung checked in will get applied to our phone. No firm conclusions yet. Even if it doesn't apply, the hope is the data we get from testing will help us produce more flexible "safe" flashing practices.

Please do NOT test CWM Touch for now. We want to isolate just the FE07 kernel and unlocked stock recovery before introducing new variables.


Executive Summary
Garwynn has found a recent checkin from Samsung in the kernel code handling EMMC memory that fixes a data corruption problem. It is possible this might fix the /data EMMC corruption we have been seeing, but we aren't sure if it is fixing the same problem. The first release to include that checked in code is FE07. There has been some communication with the developers in charge of that area to gather further info.

This thread's purpose is to foster discussion on the issue and to determine if the potential fix actually does fix our issue. Even if the fix doesn't address the issue, it is hoped in the process we are able to gather more info into specific "safe" and "unsafe" scenarios.

Please do NOT jump ahead and think it is fixed. It is TOO EARLY to make that claim.


Background
As many of you are aware since ICS has come out, there has been a nagging issue where in some situations flashing ROMs with an ICS-based kernel and custom recovery has left the phone with EMMC corruption. This EMMC corruption is so far non-recoverable, even with JTAG bit blasting, which should bypass all but hardware issues.

This problem is NOT limited to the Epic 4G Touch. Other GS2 models as well as Galaxy Note are experiencing the same thing as can be seen by this Public Service Announcement in the Galaxy Note section.

The problem first cropped up when people used ROM Manager to temporary "fake" flash CWM Touch onto an ICS-based kernel to do their flashing needs. In particular wipe data/factory reset seemed to often trigger the /data EMMC corruption. However later we found it wasn't limited to just CWM Touch and temporary flashing as CWM repacks with the ICS-based kernel also exhibited that behavior, albeit not as often.

Even more frustrating is that this bug is not always deterministic, in that you could do some operation 3 times and have it work fine, then on the 4th, trigger the /data EMMC corruption.

Complicating the testing/debugging is the issue that once the problem is triggered, your phone is basically not recoverable. You can try and ODIN a stock ROM on top which will basically work for all the components except the /data partition. Once it reaches the /data partition, ODIN will hang. Similarly if you try and wipe data/factory reset, it will hang or timeout after a while. Attempts to repartition and reformat using ODIN have not changed this behavior. Attempts to edit the partition info manually have not been successful. JTAG bit blasting has not been successful.

You can read about the past experiences in the Stuck at "Data.img" thru odin thread. By the time you get to ODIN, the damage to /data EMMC is already done. ODIN is NOT causing the damage. ODIN is hanging on data.img because the hardware won't let it write successfully to that area of EMMC.

This has led to many custom ROMs giving special procedures to go back to a GB-based kernel repacked with CWM recovery to do all your flashing (EL26+CWM). It is also the motivation for the How Not To Brick Your E4GT thread.


Details
The code checkin that has piqued our interest is in regards to data corruption caused by problem in the wear-level firmware code of the emmc. This is low-level code that runs on a processor in the emmc module. It basically tries to spread out the data writes so you get an even distribution of writes so as any one section of emmc memory does not get worn out prematurely. This code apparently can corrupt data by writing 32KB of incorrect data under some situations.

https://bitbucket.org/franciscofranco/android-tuna-omap/changeset/cea631bdac53

The code appears to restrict the firmware fix to only certain "affected" emmc modules. Also it is not able to persistently/permanently patch the firmware so this code must run at each startup. The following modules were identified in the code:

Name: VYL00M
HwRev: 0x0
FwRev: 0x25

Name: KYL00M
HwRev: 0x0
FwRev: 0x25

Name: MAG4FA
HwRev: 0x0
FwRev: 0x25

Unfortunately during ad-hoc polling we have found a case of an EMMC /data bricked phone with fwrev 0x0, so either we are not understanding what Samsung's fix is doing or they may not have addressed the full scope of the problem. Do NOT assume if your fwrev is 0x0 you are safe.

At this point, this does NOT mean the fix is not applicable. We might be looking at the wrong data. The kernel might not be exporting the data to us. The fix might need to be expanded to more modules. The fix could be for something else entirely but we might be able to avoid the bug anyway using stock recovery.

To determine what version you have (keep in mind we are at the preliminary stage, so this info might not be the right info to collect or could be meaningless for the /data EMMC corruption issue)
[email protected]:/ $ su
[email protected]:/ # cd /sys/class/block/mmcblk0/device

[email protected]:/sys/class/block/mmcblk0/device # cat name hwrev fwrev manfid oemid date type serial cid
MAG4FA
0x0
0x0
0x000015
0x0100
08/2011
MMC
0xd3f24fe6
1501004d414734464119d3f24fe68e8b

The comments for the code checkin give the following info:
/*
* There is a bug in some Samsung emmc chips where the wear leveling
* code can insert 32 Kbytes of zeros into the storage. We can patch
* the firmware in such chips each time they are powered on to prevent
* the bug from occurring. Only apply this patch to a particular
* revision of the firmware of the specified chips. Date doesn't
* matter, so include all possible dates in min and max fields.
*/

The critical piece of code appears to be the following:
Code:
	/* set value 0x000000FF : It's hidden data
	 * When in vendor command mode, the erase command is used to
	 * patch the firmware in the internal sram.
	 */
	err = mmc_movi_erase_cmd(card, 0x0004DD9C, 0x000000FF);
	if (err) {
		pr_err("Fail to Set WL value1\n");
		goto err_set_wl;
	}
	/* set value 0xD20228FF : It's hidden data */
	err = mmc_movi_erase_cmd(card, 0x000379A4, 0xD20228FF);
	if (err) {
		pr_err("Fail to Set WL value2\n");
		goto err_set_wl;
	}

Action items
At this point we would like to

1) gather more info on which emmc modules folks have and see if we can detect any patterns, so if you could post your EMMC info and optionally include whether you have the ability to do testing (presumably because you have a way to replace your phone if it is damaged)

2) solicit one volunteer to try different flashing scenarios using the unlocked stock recovery and FE07 kernel repack (bigpeng indicated earlier he would be willing to do this for the community, but that was before the fwrev info, so he might have had a false sense of security, so no pressure on him if he changed his mind)

If we find that the volunteer does not see any corruption despite trying to do so, then we can expand testing to a few more people and also work on getting CWM repacks.

If the volunteer hits the bug, then we will know the issue is still there even with stock recovery and FE07 kernel.

Keep in mind, at some point someone will need to take one for the team or we will be forever in fear of bricking our phones using ICS-based kernels.


Resources

1) FE07-based repacks
Unlocked Recovery Only [update.zip / tar]
Plus (unlocked recovery, init.d, adb-root) [update.zip / tar]

2) FE10-based repacks
Unlocked Recovery Only [update.zip / tar]
Plus (unlocked recovery, init.d, adb-root) [update.zip / tar]

3) JEDEC eMMC documentation

Related threads
Galaxy Note CID investigation thread
 
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Azrael.arach

Senior Member
Jul 5, 2010
190
27
This is mine. I can try to help but not till weekend when my other phone gets here.

MAG4FA
0x0
0x0
0x000015
0x0100
11/2011
MMC

Sent from my SPH-D710 using Tapatalk 2
 
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krazyflipj

Senior Member
Jan 14, 2008
2,827
440
Full readings from my /data bricked device. Let me know if you want me to check anything else out:


MAG4FA
0x0
0x0
0x000015
0x0100
08/2011
MMC
 

garwynn

Retired Forum Mod / Inactive Recognized Developer
Jul 30, 2011
5,182
8,589
NE Ohio
www.extra-life.org
Sorry for the delay on giving more details. I've got info that I'll be passing along soon, just want to read up on something a little more before I post it out here.

Regardless whether this fix turns out to be related to the issue we've been looking at, I want to throw this in now before getting into the weeds:

Big thanks to Ken Sumrall from the Android team as he's been good enough to share info with us about this bugfix. As the person who signed off on the change commit he's one of the best resources on this issue. Also want to give credit to Mr. Min of Samsung who developed the fix in question.

I'll be posting more shortly. Those with dev experience, particularly with C++ and/or Assembly may be able to help us as well.
 

garwynn

Retired Forum Mod / Inactive Recognized Developer
Jul 30, 2011
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NE Ohio
www.extra-life.org
Source Notes - Part 1

Source Notes - Part 1
(Please feel free to skip if you're not interested in the programming)

This section is just to document what models and versions are affected.
I'm posting this in rather lengthy detail in part for peer review and also as I misread this the first time.
If you want to see the results of this documentation you can skip to the bottom.

Again, you'll need the link to the change:
https://bitbucket.org/franciscofranco/android-tuna-omap/changeset/cea631bdac53

If I look at this part of code alone:
Code:
cid_rev(0, 0x25, 1997, 1)

...this tells me to look for a definition of cid_rev. So I do and get here:
Code:
#define cid_rev(hwrev, fwrev, year, month)      \
        (((u64) hwrev) << 40 |                  \
         ((u64) fwrev) << 32 |                  \
         ((u64) year) << 16 |                   \
         ((u64) month))

It's not included in this change as this was introduced previously.
But you can see the definition here:
https://bitbucket.org/franciscofranco/android-tuna-omap/src/388ae9aa9b26/include/linux/mmc/card.h

OK, so I should look for HW revision 0x0, FW revision 0x25, right?
Nope. This was nested in another function and I didn't look at that right:
Code:
	MMC_FIXUP_REV("VYL00M", 0x15, CID_OEMID_ANY,
		      cid_rev(0, 0x25, 1997, 1), cid_rev(0, 0x25, 2012, 12),
		      add_quirk_mmc, MMC_QUIRK_SAMSUNG_WL_PATCH),
	MMC_FIXUP_REV("KYL00M", 0x15, CID_OEMID_ANY,
		      cid_rev(0, 0x25, 1997, 1), cid_rev(0, 0x25, 2012, 12),
		      add_quirk_mmc, MMC_QUIRK_SAMSUNG_WL_PATCH),
	MMC_FIXUP_REV("MAG4FA", 0x15, CID_OEMID_ANY,
		      cid_rev(0, 0x25, 1997, 1), cid_rev(0, 0x25, 2012, 12),
		      add_quirk_mmc, MMC_QUIRK_SAMSUNG_WL_PATCH),

OK, so back to the card.h file to get my definition of MMC_FIXUP_REV:

Code:
#define MMC_FIXUP_REV(_name, _manfid, _oemid, _rev_start, _rev_end,     \
                      _fixup, _data)                                    \
        _FIXUP_EXT(_name, _manfid,                                      \
                   _oemid, _rev_start, _rev_end,                        \
                   SDIO_ANY_ID, SDIO_ANY_ID,                            \
                   _fixup, _data)                                       \

I also want to look at _FIXUP_EXT next:
Code:
#define _FIXUP_EXT(_name, _manfid, _oemid, _rev_start, _rev_end,        \
                   _cis_vendor, _cis_device,                            \
                   _fixup, _data)                                       \
        {                                                  \
                .name = (_name),                           \
                .manfid = (_manfid),                       \
                .oemid = (_oemid),                         \
                .rev_start = (_rev_start),                 \
                .rev_end = (_rev_end),                     \
                .cis_vendor = (_cis_vendor),               \
                .cis_device = (_cis_device),               \
                .vendor_fixup = (_fixup),                  \
                .data = (_data),                           \
         }

So to properly identify what is affected:

Model Name (.name) -> VYL00M, KYL00M or MAG4FA
Manu. Firwmare ID Manufacturer ID: --> 0x15
OEM ID: Any ID (easy extrapolation of CID_OEMID_ANY)
Revision Start (Range): The result of cid_rev(0, 0x25, 1997, 1). The date indicates a low limit value.
Revision End (Range: The result of cid_rev(0, 0x25, 2012, 12). The date indicates a high limit value.
Fixup: Function to call to add the fixup - in this case, add_quirk_mmc (data.h linked above)
Data: MMC_QUIRK_SAMSUNG_WL_PATH (Not 100% but looks like a label to me. Can't find a definition in change.)

Note:
The fix mentioned right above the models affected in a note: "Date doesn't matter, so include all possible dates in min and max fields." I misread how they were getting the low and high limits of the range.


The corrected eMMCs affected involve VYL00M, KYL00M or MAG4FA at Manufacturer Firmware ID 0x15.

I would like to apologize for providing inaccurate info the first time; after going through the code another time I'm fairly certain the correction to the affected model list is accurate.

This also confirms that those who have posted are in the affected list, which we knew but couldn't confirm until now.
 
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Azrael.arach

Senior Member
Jul 5, 2010
190
27
So does this mean the new code in the kernel is to help this problem and what would be the steps to testing it?

Sorry if dumb questions, just trying to learn.

Sent from my SPH-D710 using Tapatalk 2
 

robertm2011

Senior Member
Dec 27, 2011
861
497
So theoretically, those of us who have posted are able to make full use of the ability to flash, backup, etc. with the proper modification to our kernels? (Hope I got this right.)

Sent from my SPH-D710 using Tapatalk 2
 

garwynn

Retired Forum Mod / Inactive Recognized Developer
Jul 30, 2011
5,182
8,589
NE Ohio
www.extra-life.org
So does this mean the new code in the kernel is to help this problem and what would be the steps to testing it?

Sorry if dumb questions, just trying to learn.
I'm of the thought that 99% of all questions are never dumb. And that 1% is extremely rare.

The thread is somewhat of peer review and discussion about what we've found and as a community possibly confirm whether this is both the bug causing the bricks (and by doing so confirming that this is the fix.)

robertm2011 said:
So theoretically, those of us who have posted are able to make full use of the ability to flash, backup, etc. with the proper modification to our kernels? (Hope I got this right.)

It means that the fix applies to those devices. What still isn't closed is whether the bug that this squishes is *the* bug (causing the ICS based bricks). I'm going to be posting more about that part here shortly for feedback and discussion.
 

azyouthinkeyeiz

Senior Member
Jan 3, 2010
675
122
/* Missed the first paragraph of the details section. Low level corruption would do what I was questioning. Nvm
Sent from my SPH-D710 using Tapatalk 2
 
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garwynn

Retired Forum Mod / Inactive Recognized Developer
Jul 30, 2011
5,182
8,589
NE Ohio
www.extra-life.org
Discussion with Android Team

OK, now on to the bug that this fixes. This post will only contain the discussions between myself and Mr. Sumrall of the Android team.

Initial inquiry to Mr. Sumrall:
Garwynn said:
1) Was the bug that this patched causing the eMMC failures on Samsung devices using an 3.0+ kernel?

2) If #1 is yes, is it known if this correct the I/O errors already experienced? Or is this perhaps preventative in nature?

Initial Response:
Ken Sumrall - Android Team said:
The bug was in the emmc firmware which ran on a small microprocessor inside the emmc chip, and it didn't matter what kernel was running on the device to which it was attached. However, it may be the case that a particular kernel version was more likely to trigger the bug.

With this patch, the bug is worked around, and the emmc chip should no longer corrupt data.

We also knew this from the code:
Code:
	 * There is a bug in some Samsung emmc chips where the wear leveling
	 * code can insert 32 Kbytes of zeros into the storage.  We can patch
	 * the firmware in such chips each time they are powered on to prevent
	 * the bug from occurring.
Note: Snipped last part of comment as it is already covered.

OK, so it's putting potentially zeros in the storage; but it doesn't give us any clues as to where the possible storage was or how this could corrupt the filesystem. So I sent some follow-up questions and got the following responses. (Regular is question to Mr. Sumrall, bold is response.

1)*Can this release fix a device where the bug has already been triggered (resulting in I/O error)?

No. *The 32 Kbytes of zeros have already been inserted into the filesystem (usually in a particularly bad place, like the inode or block bitmaps, or the inode table) and the filesystem is now corrupt.

2) What would happen if a device is rolled back to a previous kernel - one without this fix? Would it be exposed again to the bug?

Yes, the corruption could happen on older kernels. *The fix doesn't permanently fix the firmware, it patches the firmware every time the device is powered on (initial power-on, wakeup from sleep).

The next question was one that has been bugging me so I figured it wouldn't hurt to learn more about this bug. Sorry if this rubs some people the wrong way.

3) The explanation in the bugfix mentions 32 Kb of zeros being added to storage. But I can't see this causing an I/O error unless it was doing this in the storage containing the instruction set. Was this somehow corrupting the I/O instruction set contained within the firmware?*I have spent several weeks defending the opinion that this was not a hardware failure but software-based.

When the ext4 filesystem detects an error, and the filesystem is set to panic or re-mount read-only on error, the function ext4_handle_error() will record an EIO *in the journal:
Code:
static void ext4_handle_error(struct super_block *sb)
{
  if (sb->s_flags & MS_RDONLY)
    return;

  if (!test_opt(sb, ERRORS_CONT)) {
    journal_t *journal = EXT4_SB(sb)->s_journal;

    EXT4_SB(sb)->s_mount_flags |= EXT4_MF_FS_ABORTED;
    if (journal)
      jbd2_journal_abort(journal, -EIO);
  }
  .
  .
  .
  .
}

So it doesn't have to be an actual low-level IO error to cause EIO to be recorded in the journal.

As for hardware vs. software failure, it is a bug in the firmware of the emmc chip, and this kernel patch enables a work-around to prevent the problem from happening.

Thanks again to Mr. Sumrall for this information. More soon.
 
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  • 70
    This post will evolve over time as more info is found:

    Latest Updates
    6/24 Custom PIT repartition workaround posted by Jaymoon.
    You lose 8GB (some of which might be further recoverable with extra work) and restores using the original PIT will lockup your phone again (a scenario that could happen if you brought your phone back to Sprint for some unrelated problem) so if you have the opportunity to get your phone replaced with little to no cost, IMO that should be your primary option.
    http://forum.xda-developers.com/showthread.php?p=27852689#post27852689

    E4GT specific PIT file here (theoretically instead of losing 8GB, you'll only lose 2GB):
    http://forum.xda-developers.com/showpost.php?p=28070569&postcount=654

    6/8 Update for other platforms waiting for fix
    Codeworkx's contact with Samsung got following response [discussion]
    Update 14:56 CEST:
    Patches will be out in form of new official ROMs and also sourcecode releases after testing, which might take some time.

    6/7 Update
    Test plan posted - see bottom of post for results so far (esoteric68, krazy_smokezalot report success)
    BIG THANKS to Esoteric68 (and robertm2011 before her) who took the plunge to benefit everyone else. She has completed the test plan and more. 6 flashes of CM9, 3 flashes of AOKP, 3 wipe data/factory resets, and 3 nandroid restores, 1 stock FF02 flash, all successful. We are ready to have more testers try out the test ROM installs. We are getting more confident the code analysis was correct.

    6/2 Update
    Less technical summary and preparation for new round of testing

    5/31 Lots of discussion on the code path detailing how the problem occurs and where to put the workaround, select posts below
    Call trace for CWM Recovery - wipe data/factory reset
    Call trace for CWM Recovery - restore
    Section of update-binary afflicted by same issue as wipe data/factory reset
    Recap of where workarounds can be placed
    MD5s of various update-binary executables
    Pros/Cons of placing workaround in kernel vs libext4_utils.a
    Are ICS nandroid backup/restores safe?
    Are ICS recoveries safe?
    Why do CM9/AOKP installs often brick in ICS but not in GB?

    5/24 Update pretty much ties up all the loose ends - Thanks Mr. Sumrall, Garwynn, Entropy, and everyone else who pitched in!
    http://forum.xda-developers.com/showthread.php?p=26521643#post26521643

    Potentially very GOOD NEWS
    It appears Sprint/Samsung tested the EMMC brick issue, confirmed the problem, and tested a fix that appears to resolve the problem:
    http://forum.xda-developers.com/showthread.php?p=26465085#post26465085
    To clarify this...in testing done over the weekend, there was a small "subtest" group which consisted of 20 devices. This group was put together STRICTLY for the propose of testing the emmc bug and fix. The devices were all programmed with the data known to have cause bricks when wiping. Of those 20, all but 6 also had the code patch to resolve that issue, so there was a possibility for 6 hard bricks, only 4 actually bricked, therefore, on the build currently being tested, the "emmc break issue" has been deemed "resolved"



    We now have an update on why this bug is happening and which PRV/fwrevs are affected. PRV/fwrev 0x19 are susceptible to the EMMC /data corruption issue (which should now be referred to as EMMC lockup issue). PRV/fwrev 0x25 has the fix for the lockup issue but has a separate 32KB of zeros data corruption issue, which is being patched in the kernel (our kernels don't have that patch). All these problems are in the EMMC firmware. It can potentially be updated, but nothing is publicly available. EMMC lockup issue is triggered on erasing the EMMC. The only piece we have not been able to explain is why GB-based kernels seem immune to the EMMC lockup problem whereas ICS seems more susceptible to the problem. Presumably both are doing ERASE commands, but possibly in slightly different ways. See these posts for more details [#1 / #2]

    To get your PRV/fwrev, you can use this (if you have busybox installed):
    [email protected]:/ $ su
    [email protected]:/ # cd /sys/class/block/mmcblk0/device

    [email protected]:/sys/class/block/mmcblk0/device # cat cid | cut -b 19,20
    19
    If you don't have busybox installed just visually parse the line, match the serial # (0xd3f24fe6 - example only - yours will be different) with the cid, and look at the 2 numbers before the serial #.
    [email protected]:/ $ su
    [email protected]:/ # cd /sys/class/block/mmcblk0/device

    [email protected]:/sys/class/block/mmcblk0/device # cat serial cid
    0xd3f24fe6
    1501004d414734464119d3f24fe68e8b

    It appears after looking at the code more closely and examining the results of the card info dumps, we do not have this fix in our kernel. It isn't clear whether the fix would resolve our /data EMMC brick issues, but the point is moot right now because we don't have the fix.

    Possible BRICK here. Please do NOT do any more testing until further notice. Please do NOT use Wipe Data/Factory Reset. It is the main difference between first and 2nd round of testing and is the current suspect

    FE10 repacks added to Resource section

    Esoteric68, azyouthinkeyeiz, and robertm2011 are testing flashing different ROMs with FE07/FE10 repacked with unlocked recovery. We all owe them our thanks for risking their phones to help the community (taking one for the team) No bricks so far.

    Separately we are still discussing whether the fix Samsung checked in will get applied to our phone. No firm conclusions yet. Even if it doesn't apply, the hope is the data we get from testing will help us produce more flexible "safe" flashing practices.

    Please do NOT test CWM Touch for now. We want to isolate just the FE07 kernel and unlocked stock recovery before introducing new variables.


    Executive Summary
    Garwynn has found a recent checkin from Samsung in the kernel code handling EMMC memory that fixes a data corruption problem. It is possible this might fix the /data EMMC corruption we have been seeing, but we aren't sure if it is fixing the same problem. The first release to include that checked in code is FE07. There has been some communication with the developers in charge of that area to gather further info.

    This thread's purpose is to foster discussion on the issue and to determine if the potential fix actually does fix our issue. Even if the fix doesn't address the issue, it is hoped in the process we are able to gather more info into specific "safe" and "unsafe" scenarios.

    Please do NOT jump ahead and think it is fixed. It is TOO EARLY to make that claim.


    Background
    As many of you are aware since ICS has come out, there has been a nagging issue where in some situations flashing ROMs with an ICS-based kernel and custom recovery has left the phone with EMMC corruption. This EMMC corruption is so far non-recoverable, even with JTAG bit blasting, which should bypass all but hardware issues.

    This problem is NOT limited to the Epic 4G Touch. Other GS2 models as well as Galaxy Note are experiencing the same thing as can be seen by this Public Service Announcement in the Galaxy Note section.

    The problem first cropped up when people used ROM Manager to temporary "fake" flash CWM Touch onto an ICS-based kernel to do their flashing needs. In particular wipe data/factory reset seemed to often trigger the /data EMMC corruption. However later we found it wasn't limited to just CWM Touch and temporary flashing as CWM repacks with the ICS-based kernel also exhibited that behavior, albeit not as often.

    Even more frustrating is that this bug is not always deterministic, in that you could do some operation 3 times and have it work fine, then on the 4th, trigger the /data EMMC corruption.

    Complicating the testing/debugging is the issue that once the problem is triggered, your phone is basically not recoverable. You can try and ODIN a stock ROM on top which will basically work for all the components except the /data partition. Once it reaches the /data partition, ODIN will hang. Similarly if you try and wipe data/factory reset, it will hang or timeout after a while. Attempts to repartition and reformat using ODIN have not changed this behavior. Attempts to edit the partition info manually have not been successful. JTAG bit blasting has not been successful.

    You can read about the past experiences in the Stuck at "Data.img" thru odin thread. By the time you get to ODIN, the damage to /data EMMC is already done. ODIN is NOT causing the damage. ODIN is hanging on data.img because the hardware won't let it write successfully to that area of EMMC.

    This has led to many custom ROMs giving special procedures to go back to a GB-based kernel repacked with CWM recovery to do all your flashing (EL26+CWM). It is also the motivation for the How Not To Brick Your E4GT thread.


    Details
    The code checkin that has piqued our interest is in regards to data corruption caused by problem in the wear-level firmware code of the emmc. This is low-level code that runs on a processor in the emmc module. It basically tries to spread out the data writes so you get an even distribution of writes so as any one section of emmc memory does not get worn out prematurely. This code apparently can corrupt data by writing 32KB of incorrect data under some situations.

    https://bitbucket.org/franciscofranco/android-tuna-omap/changeset/cea631bdac53

    The code appears to restrict the firmware fix to only certain "affected" emmc modules. Also it is not able to persistently/permanently patch the firmware so this code must run at each startup. The following modules were identified in the code:

    Name: VYL00M
    HwRev: 0x0
    FwRev: 0x25

    Name: KYL00M
    HwRev: 0x0
    FwRev: 0x25

    Name: MAG4FA
    HwRev: 0x0
    FwRev: 0x25

    Unfortunately during ad-hoc polling we have found a case of an EMMC /data bricked phone with fwrev 0x0, so either we are not understanding what Samsung's fix is doing or they may not have addressed the full scope of the problem. Do NOT assume if your fwrev is 0x0 you are safe.

    At this point, this does NOT mean the fix is not applicable. We might be looking at the wrong data. The kernel might not be exporting the data to us. The fix might need to be expanded to more modules. The fix could be for something else entirely but we might be able to avoid the bug anyway using stock recovery.

    To determine what version you have (keep in mind we are at the preliminary stage, so this info might not be the right info to collect or could be meaningless for the /data EMMC corruption issue)
    [email protected]:/ $ su
    [email protected]:/ # cd /sys/class/block/mmcblk0/device

    [email protected]:/sys/class/block/mmcblk0/device # cat name hwrev fwrev manfid oemid date type serial cid
    MAG4FA
    0x0
    0x0
    0x000015
    0x0100
    08/2011
    MMC
    0xd3f24fe6
    1501004d414734464119d3f24fe68e8b

    The comments for the code checkin give the following info:
    /*
    * There is a bug in some Samsung emmc chips where the wear leveling
    * code can insert 32 Kbytes of zeros into the storage. We can patch
    * the firmware in such chips each time they are powered on to prevent
    * the bug from occurring. Only apply this patch to a particular
    * revision of the firmware of the specified chips. Date doesn't
    * matter, so include all possible dates in min and max fields.
    */

    The critical piece of code appears to be the following:
    Code:
    	/* set value 0x000000FF : It's hidden data
    	 * When in vendor command mode, the erase command is used to
    	 * patch the firmware in the internal sram.
    	 */
    	err = mmc_movi_erase_cmd(card, 0x0004DD9C, 0x000000FF);
    	if (err) {
    		pr_err("Fail to Set WL value1\n");
    		goto err_set_wl;
    	}
    	/* set value 0xD20228FF : It's hidden data */
    	err = mmc_movi_erase_cmd(card, 0x000379A4, 0xD20228FF);
    	if (err) {
    		pr_err("Fail to Set WL value2\n");
    		goto err_set_wl;
    	}

    Action items
    At this point we would like to

    1) gather more info on which emmc modules folks have and see if we can detect any patterns, so if you could post your EMMC info and optionally include whether you have the ability to do testing (presumably because you have a way to replace your phone if it is damaged)

    2) solicit one volunteer to try different flashing scenarios using the unlocked stock recovery and FE07 kernel repack (bigpeng indicated earlier he would be willing to do this for the community, but that was before the fwrev info, so he might have had a false sense of security, so no pressure on him if he changed his mind)

    If we find that the volunteer does not see any corruption despite trying to do so, then we can expand testing to a few more people and also work on getting CWM repacks.

    If the volunteer hits the bug, then we will know the issue is still there even with stock recovery and FE07 kernel.

    Keep in mind, at some point someone will need to take one for the team or we will be forever in fear of bricking our phones using ICS-based kernels.


    Resources

    1) FE07-based repacks
    Unlocked Recovery Only [update.zip / tar]
    Plus (unlocked recovery, init.d, adb-root) [update.zip / tar]

    2) FE10-based repacks
    Unlocked Recovery Only [update.zip / tar]
    Plus (unlocked recovery, init.d, adb-root) [update.zip / tar]

    3) JEDEC eMMC documentation

    Related threads
    Galaxy Note CID investigation thread
    30
    I posted this less technical writeup on agat63's cwm repacked thread but figured it would be useful to have here also. I am working with CM9/AOKP to have their install scripts replace format("/system") with delete_recursive("/system") After that I think if we still have volunteers, we are ready to do some more testing.

    I'll provide more details when the pieces become available, but if you'd like to take one for the team and help test, please post. If our understanding of the problem is accurate, you should be safe this time around, but there is always the chance we are not understanding the problem completely.

    ====

    I would like to stress that the information I gave agat was based on code tracing and NOT based on real-world testing. You should treat this as a *testing period* to confirm the analysis. You MAY BRICK if the analysis is incorrect.

    The following is all assuming you are repacked with ICS kernel (ie we aren't talking about the GB kernel)...

    Background
    The nature of the problem is a call to the function make_ext4fs(). This function isn't provided by the kernel, rather it is provided as a library (libext4_utils.a) that is used when compiling Recovery and the update installer. It does end up eventually calling kernel mmc driver routines, which then trigger the EMMC firmware lockup/superbrick bug.

    The make_ext4fs() function changed between GB and ICS. In GB the function didn't try to erase the partition before creating the EXT4 fs. In ICS it tries to erase it first. The erase is triggering an EMMC firmware bug that was always there via the kernel MMC driver. GB is also "doubly" safe in that not only do Recovery and update-binary never attempt to do the erase, even if they did, the request to erase is blocked in the GB-kernel and never run.

    The EMMC firmware bug will lockup your phone and corrupt internal EMMC meta-data which cannot be accessed or repaired at this time. It isn't crashing your hard drive per-se, it is crashing your hard drive controller in a way that prevents the hard drive controller from accessing parts of your disk. We don't have any way of updating the EMMC hard drive controller at this time.

    The EMMC firmware lockup/superbrick bug is likely contained in the wear-level firmware code which shifts mmc-internal memory block usage around to prevent any one area from overuse. The bug MIGHT NOT be triggered every time, so you can do the same operation with no issues then on your Nth attempt it bricks.

    Details
    So what does that mean for you? There are 2 executables we are concerned with, Custom Recovery and the update installer (update-binary)

    Custom Recovery is responsible for 2 potential bricking points:
    1) wipe data/factory reset
    2) nandroid backup/restore

    These are both handled by the Recovery itself so if your Recovery is "safe" then these operations should be safe. The nandroid backup is safe regardless. Our concern is only for wipe data/factory reset and nandroid restore. Both of these make the call to make_ext4fs(), so if they are using the GB-based version they are safe. If they are using the ICS version, they are not safe (when used with ICS kernel) Agat has made the effort to make sure the recovery he has provided is compiled against GB CM7 source.

    You may ask what about Installing ROMs, you thought Recovery was responsible for that too?
    This is only partially true. You use the menu option in Recovery to choose to install an update.zip. Recovery is responsible for providing the location of the update.zip and verifying the signature, but when it comes to actually "installing" the update.zip, Recovery uses a "helper app" called update-binary contained in the update.zip.

    This update-binary helper app is responsible for running the Edify install script in the update.zip. It communicates with Recovery just to update the progress bar, output ui messages, and set up the updating of firmware. The rest of the script functions, it handles by itself directly, so Recovery isn't involved.

    update-binary also calls make_ext4fs() so it can also do potentially "unsafe" operations, just like we discussed for Recovery above. If the update-binary, that was included in the update.zip, was compiled using GB-sources, then it is "safe". If it was compiled against ICS sources then there is one function in the Edify script that can potentially cause bricking, format().

    To be clear, Recovery has no control over the update-binary that is included in the update.zip. Whomever built the ROM update.zip package made that decision. So this is why even with a "safe" Recovery, you can brick your phone installing ROMs (with an ICS kernel).

    Even if the Recovery is "safe", if you ask it to use an "unsafe" update-binary to install a ROM AND that ROM install script chose to do a format(), then the EMMC lockup/superbrick bug can be triggered.

    The reason why most stock-based ROMs don't brick in ICS is because
    1) most of them probably include a GB-based update-binary
    2) most of them are not performing a format() within their Edify updater-script

    So a ROM builder has 2 ways to make a ROM update.zip install "safe" to install in ICS. Either package a known GB-based update-binary OR eliminate format(), if present, from the Edify install script.

    So why does Calk's format_all seem to never brick even on ICS? Given the date on the update-binary and when he created the package, it is most likely using a GB-based update-binary

    So why does CM9/AOKP seem to brick more often than stock-based ICS ROM installs? The Edify install script for CM9/AOKP uses new functions that were introduced in the ICS update-binary. This in turn is why they bundle the ICS-based update-binary. They could still potentially be safe, but in the install script a format("/system") is performed. If that format is run under an ICS kernel it will trigger the EMMC firmware lockup/superbrick bug. Under a GB-kernel, the request to erase "/system" is blocked by the GB-kernel.

    What can CM9/AOKP do to make their installs "safe" to install in ICS? All they need to do is replace the format("system") with delete_recursive("/system"). They could also replace the ICS-based update-binary with a GB-based update-binary, but that would require more rewrites to the install script. Replacing the format() call is simpler/easier.

    Why are some superbricks blue-light specials and others only make ODIN hang at data.img? This likely has to do with whether you got your brick from

    1) the format() in the CM9/AOKP install
    2) restoring nandroid backup
    3) doing the wipe data/factory reset in Recovery

    The first two tend to be blue-light specials as they affect /system and/or kernel. The last one tends to affect /data and/or /cache.

    So how do you make sure you are totally safe?
    1) make sure you are using a "safe" recovery repacked with the stock ICS kernel. This is a Recovery that was compiled against GB-based libext4_utils.a (ie GB source) This will assure you that wipe data/factory reset and nandroid restores are safe
    2) whenever you install a ROM for the first time, verify EITHER
    a) the ROM install script is NOT performing any format() calls
    b) the ROM install has bundled a GB-based update-binary

    If neither 2a NOR 2b are true (ie ICS-based update-binary and install performs format) then you DO NOT want to flash that ROM in Recovery while on an ICS kernel. Flash that ROM on a GB-based kernel/recovery.

    Hope that clears things up, and once again, remember, this analysis is only based on tracing code. I may have made a mistake in the analysis or our understanding of the problem could be wrong. We will not be sure if all these statements hold UNTIL WE DO REAL-WORLD TESTING.
    19
    Morning Update

    Well, it's been some time but thankfully Mr. Sumrall from Android did get back to us on our questions. I think the community will find that this was worth the wait.

    Issue: fwrev not set properly.
    As we suspected the bugfix is not in our build. (The patch applies this unconditionally.)
    Ken Sumrall said:
    The patch includes a line in mmc.c setting fwrev to the rights bits from the cid register. Before this patch, the file /sys/class/block/mmcblk0/device/fwrev was not initialized from the CID for emmc devices rev 4 and greater, and thus showed zero.

    (On second inquiry)
    fwrev is zero until the patch is applied.

    Question: Revision didn't match the fix
    (Emphasis mine in red as it discusses the superbrick issue.)
    Ken Sumrall said:
    You probably have the bug, but rev 0x19 was a previous version of the firmware we had in our prototype devices, but we found it had another bug that if you issued an mmc erase command, it could screw up the data structures in the chip and lead to the device locking up until it was powered cycled. We discovered this when many of our developers were doing a fastboot erase userdata while we were developing ICS. So Samsung fixed the problem and moved to firmware revision 0x25. Yes, it is very annoying that 0x19 is decimal 25, and that led to lots of confusion when trying to diagnose emmc firmware issues. I finally learned to _ALWAYS_ refer to emmc version in hexadecimal, and precede the number with 0x just to be unambiguous.

    However, even though 0x19 probably has the bug that can insert 32 Kbytes of zeros into the flash, you can't use this patch on devices with firmware revision 0x19. This patch does a very specific hack to two bytes of code in the revision 0x25 firmware, and the patch most likely will not work on 0x19, and will probably cause the chip to malfunction at best, and lose data at worst. There is a reason the selection criteria are so strict for applying this patch to the emmc firmware.

    I passed on our results a few days later mentioning that the file system didn't corrupt until the wipe. This is a response to that follow-up.

    As I mentioned in the previous post, firmware rev 0x19 has a bug where the emmc chip can lockup after an erase command is given. Not every time, but often enough. Usually, the device can reboot after this, but then lockup during the boot process. Very rarely, it can lockup even before fastboot is loaded. Your tester was unlucky. Since you can't even start fastboot, the device is probably bricked. :-( If he could run fastboot, then the device could probably be recovered with the firmware update code I have, assuming I can share it. I'll ask.

    Question: Why the /data partition?
    Ken Sumrall (Android SE) said:
    Because /data is the place the chip that experiences the most write activity. /system is never written to (except during an system update) and /cache is rarely used (mostly to receiving OTAs).

    Question: Why JTAG won't work?
    Ken Sumrall said:
    As I mention above, the revision 0x19 firmware had a bug that after an emmc erase command, it could leave the internal data structures of the emmc chip in a bad state that cause the chip to lock up when a particular sector was accessed. The only fix was to wipe the chip, and update the firmware. I have code to do that, but I don't know if I can share it. I'll ask.

    Question: Can a corrupted file system be repaired (on the eMMC)?
    Ken Sumrall said:
    e2fsck can repair the filesystem, but often the 32 Kbytes were inserted at the start of a block group, which erased many inodes, and thus running e2fsck would often result in many files getting lost.

    So, while the fix doesn't apply to us at the moment, we've been given a great insight into the superbrick issue as well as information that a fix is already developed (hopefully we'll see it released!). The bug likely applies to us and assuming the fix for the 0x19 firmware is given then it would apply to our devices.

    On a lighter note, I wanted to include his close:
    Ken Sumrall said:
    You are getting a glimpse into the exciting life of an Android kernel developer. :) Turns out the job is mostly fighting with buggy hardware. At least, it seems that way sometimes.
    18
    5/24 Update

    Fresh off the press...

    Q: Do you know the commands to reset the eMMC controller in question?
    Ken Sumrall (Android) said:
    Once the chip has locked up, no command will reset it. It must be power cycled. If instead you are asking how to clear the metadata so the chip works again, the only solution I know is to update the firmware inside the chip, and that also wipes all the data. This probably includes factory calibration data that must be saved before the firmware is updated, and restored after. Also, the boot loader is probably in the chip, and must be restored after the firmware update, or the device will be bricked. This is a dangerous operation, because if something goes wrong, the device will probably be bricked. (emphasis added)

    Q: Is there any documentation available on this issue? If so and it is private is it possible to have it released?
    Ken Sumrall (Android) said:
    It is private, I'm asking if I can release it, along with the code to update the emmc firmware. Don't get your hopes up, my guess is the answer will be no.

    Q: Alternate erase method?
    Ken Sumrall (Android) said:
    If you really want to erase data on a rev 0x19 samsung emmc chip, I suggest you just write zeros to the entire partition.

    Q: Difference between GB/ICS Wipe
    Ken Sumrall (Android) said:
    IIRC, when using recovery to wipe the phone on GB, the make_ext4fs() library would not issue an erase command first, it would just write one a new blank filesystem. This, of course, doesn't really erase all the private data of the user, so we changed make_ext4fs() to first erase the partition, then write out the new filesystem. You can see the code in system/extras/ext4_utils/wipe.c, which didn't exist in gingerbread, but does in honeycomb and later. It is the erase operation on the rev 0x19 firmware that can cause the emmc chip to lockup. (emphasis added)

    Regarding Entropy512's summary of observations:
    Ken Sumrall (Android) said:
    Regarding the notes on MMC_CAP_ERASE, the just lists the cards ability to perform the erase command. In other words, if the mmc_erase() function works. What is more important is if anyone calls the mmc_erase() function. Looking at the mmc driver, in drivers/card/block.c, it is only called when a secure discard or discard request is made. As far as I know, those requests are only sent if the filesystem is mounted with the "discard" option, or if userspace code does an ioctl() to erase a partition, like make_ext4fs does. So check the mount options on the filesystems. *If they don't specify "discard", the erase operations are probably not happening.

    Of course, a simple debugging printk() in the mmc_erase() function will tell you if anyone is calling it.

    Additional info not directly related to questions:
    Ken Sumrall (Android) said:
    The lockup doesn't happen immediately after power-on. The chip doesn't lock up until a sector is referenced that has corrupted wear leveling data inside the chip. Once that sector is referenced, the chip will lockup hard, and the only thing that will get it talking again is to power cycle it. Once it is power cycled, the chip will talk again, until that bogus sector is accessed.
    16
    I was able to confirm with chris41g and T.C.P that the update-binary, included with both the CM9 and AOKP ROM update.zip files, was compiled against ICS source code.

    This means that this update-binary can potentially trigger the EMMC firmware lockup/superbrick bug if "format()" is used in the Edify install script. Both CM9 and AOKP updater-script format("/system") as part of their installs.

    This explains why they brick so often with the bluelight-only style brick, it is because the format("/system") elicits the lockup when make_ext4fs() is called on the /system partition and eventually results in an mmc_erase(). With a boarked /system, you are left with the blue-light special and ODIN will hang on factoryfs.img.

    The other style of brick is the one that hangs on the logo. That one is caused by Wipe Data/Factory Reset from an "unsafe" cWM Recovery. Just as above, the "unsafe" CWM Recovery would have been compiled against the ICS libext4_utils.a and make_ext4fs() would be called on /data and /cache. Eventually that would lead to mmc_erase() being called. With a boarked /data, you are left with a phone that hangs on the log and ODIN will hang on data.img

    As an aside, I now believe the main "unsafe" Recovery we were dealing with was CWM Touch fake-flashed onto the ICS kernel. I don't have the source code for CWM Touch, but I believe it was compiled against the ICS libext4_utils.a. I am not sure if Rogue CWM repacked with an ICS kernel was compiled against ICS sources, but the version that Steady checked into github was not.

    Now previously I recall discussions where it was determined that GB source/kernels also had mmc_erase() and it was an open question why, if both GB and ICS had mmc_erase(), Recovery Wipe Data/Factory Reset would brick one but not the other. Well we finally got the answer to that, the GB version of make_ext4fs() from libext4_utils.a did not perform the ioctl() calls which would eventually lead to mmc_erase() being called, while the ICS version of libext4_utils.a had the ioctl() calls.

    Now if you've been following closely so far, you may be wondering why if the update-binary that is bundled with both CM9 and AOKP ROM update.zip files is using the ICS version of libext4_utils.a (that makes the ioctl() calls which lead to mmc_erase()) it doesn't brick when run under a GB-kernel/CWM. Both ICS and GB have mmc_erase() functionality so it should brick both right?

    Well I wondered the same thing, went digging a little, and believe have found the answer.

    It turns out that even though the GB kernel MMC driver has mmc_erase() the ioctl() calls that would eventually lead to mmc_erase() being called were ifdef'd out. So if you had an "unsafe" update-binary which made the ioctl() calls, they would NOT result in mmc_erase() being called when the ROMs update.zip was run under a GB kernel/recovery.

    Previously the discussion centered around MMC_CAP_ERASE as the explanation, which I believe is a red-herring. This is neither a pre-processor directive nor a direct control mechanism. It is a bit field used to specify whether an MMC device supports the capability of doing erases. It was not ifdef'd out of GB so the functionality was still there.

    The actual conditional compile was on the ioctl() function for mmc cards, which was basically disabled under GB kernels. This is how I came to that conclusion:

    Notice in the kernel config file Samsung provided, both CONFIG_MMC_DISCARD and CONFIG_TARGET_LOCALE_NTT are disabled.

    .config
    Code:
    # CONFIG_MMC_DEBUG is not set
    [B][U]# CONFIG_MMC_DISCARD is not set[/U][/B]
    CONFIG_MMC_UNSAFE_RESUME=y
    # CONFIG_MMC_EMBEDDED_SDIO is not set
    # CONFIG_MMC_PARANOID_SD_INIT is not set
    Code:
    # CONFIG_MACH_C1_NA_SPR_EPIC2_REV00 is not set
    # CONFIG_TARGET_LOCALE_EUR is not set
    # CONFIG_TARGET_LOCALE_KOR is not set
    [B][U]# CONFIG_TARGET_LOCALE_NTT is not set[/U][/B]
    CONFIG_TARGET_LOCALE_NA=y

    Now if you look at the mmc block device driver, due to the kernel config above, the ioctl() function call in the function table is left unpopulated. This basically means ioctl() calls are not supported for the mmc device (based on E4GT GB source, don't know about other platforms).

    drivers/mmc/card/block.c
    Code:
    static const struct block_device_operations mmc_bdops = {
    	.open			= mmc_blk_open,
    	.release		= mmc_blk_release,
    [B][U]#ifdef CONFIG_MMC_DISCARD[/U][/B]
    	.ioctl			= mmc_blk_ioctl,
    [B][U]#endif[/U][/B]
    [B][U]#if defined(CONFIG_TARGET_LOCALE_NTT)[/U][/B]
    #if 0 //def CONFIG_MMC_CPRM
    	.ioctl			= mmc_blk_ioctl,	//int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);  in blkdev.h
    #endif
    [B][U]#endif[/U][/B]

    Now when the "unsafe" update-binary from CM9/AOKP is paired with a GB kernel the wipe.c from libext4_utils.a will try and make these calls:

    system/extras/ext4_utils/wipe.c
    Code:
    int wipe_block_device(int fd, s64 len)
    {
      u64 range[2];
      int ret;
    
      range[0] = 0;
      range[1] = len;
    
      ret = [B][U]ioctl(fd, BLKSECDISCARD, &range);[/U][/B]
    
      if (ret < 0) {
        range[0] = 0;
        range[1] = len;
        ret = [B][U]ioctl(fd, BLKDISCARD, &range);[/U][/B]
      }
      return 0;
    }

    I believe that both those calls have basically been disabled because ioctl() calls are not supported in the mmc block device driver under the GB kernel (for E4GT EL29 GB kernel source).

    So what does that all mean?

    I believe GB systems are doubly "safe". The kernel will not execute mmc_erase() even though the functionality is there because the ioctl() call entry point from user space to kernel space has been disabled and also GB recovery and GB update-binary never even attempt to make the ioctl() calls.

    That explains why, if you pair an "unsafe" update-binary from the CM9/AOKP ROM update.zip with a GB kernel, it is still safe.