[Kernel][5.x][carcosa-kernel][Stock kernel with cherry-picked features][2015/03/20]

1. Motivation/overview

This is a kernel for the 2012 Nexus 7 (grouper/tilapia) which sticks as closely as possible to the stock/released kernel sources, while incorporating the features I want from other popular alternative kernels. I've built it because my Nexus 7 3G (tilapia) has trouble with all of the non-stock kernels I've tried -- something causing USB resets in a tight loop. I rebuilt the stock kernel and started adding my favorite features in order to rule out what was causing the problem, but ended up with a kernel I preferred for day-to-day use.

You might like it, too.

Note that there is very little original content in this kernel: see the credits below and the github repository for the sources of the included features.

2. Features

IO Schedulers

1. bfq
2. row
3. SIO

CPU Governors

1. smartmax
2. wheatley

Misc

1. Build with -Os (optimize for size)
2. GPU overclock
3. Experimental: remove baseband_xmm_power wakelock
4. f2fs driver (see note in second post)
5. ntfs r/w (see note in second post)
6. CPU voltage control
7. Mount slave namespace workaround
8. CPU overclock (against my better judgement).

3. Instructions

This kernel is intended primarily for use with the stock ROM. The first releases (mr1 and a20) were built with a stock ramdisk, and will generally not work on other ROMs. Later releases use an AnyKernel updater and may work on other ROMs. I am only able/willing to test on stock, however, so non-stock users, use at your own risk (even more than usual).

To install, boot into your custom recovery of choice and install one of the zips below. Or use Flashify. Be sure to make a backup with your recovery first.

4. Warning and disclaimer

I am not responsible for any harm caused to you, your tablet, or the integrity of the space-time continuum by this kernel. In the words of the GNU Public License:



5. Downloads

Milestone releases:
mr1: carcosa-kernel-mr1.zip

Alpha releases:
a20: carcosa-kernel-a20.zip
Includes experimental patch removing baseband_xmm_power wakelock.
a22: carcosa-a22-anykernel.zip
Includes changes to governor defaults, ntfs r/w support, and the f2fs driver.
a23: carcosa-a23-anykernel.zip
Includes voltage control (undervolting) interface.
a25: carcosa-kernel-a25.zip carcosa-a25-anykernel.zip
Includes mount slave namespace workaround, CPU overclocking (against my better judgement)
a27: carcosa-a27-anykernel.zip
4.4.3 update
a28: carcosa-a28-anykernel.zip
Remove baseband_xmm_power wakelock again, rather than making it time out.
a29: carcosa-a29-anykernel.zip
Add configurable baseband_xmm_power wakelock timeout
a33: carcosa-a33-lp-anykernel.zip
Lollipop update; adds SIO IO scheduler.
a35: carcosa-a35-lp-anykernel.zip
Lollipop 5.1 update (still works with 5.0.2). Adds hardware acceleration for kernel encryption routines.
6. Source

Sources are on github, which is also your best source for changelogs.

7. Credits

This kernel contains precious little original work -- it builds on the stock kernel release and applies cherry-picked patches from various sources, principally M-Kernel (Metallice) Franco-kernel (Francisco Franco), and Oxydo (Sgt. Meow), but also Faux123, Ezekeel, Maxwen, and many others. My main contributions have been picking the things I wanted, and resolving the occasional hairy merge. I have attempted to maintain the original authorship information in my git logs as much as possible; I apologize for any cases where the attribution of a particular patch has been lost.

Notes

F2FS support

While this kernel (from a22 on) includes the f2fs driver, it does not include any of the ramdisk or init tweaks that you would need to use f2fs. This is because I am not in a position to test f2fs myself. That said, the a22 (and later) kernel installer will not disturb any changes you have already made to your ramdisk or ROM to support f2fs, so if you have already got f2fs working on your device, it should continue to work after installing this kernel. Don't forget to do a nand backup in your recovery before installing, though. Seriously.

NTFS R/W support

This kernel (from a22 on) includes RW support for NTFS. However, in KitKat, NTFS USB drives mounted with StickMount are not writable due to SELinux policy. To write to an NTFS USB drive, you need to (from a root shell) 'setenforce off', then 'setenforce on' when you're done using it. I do not recommend that you put SELinux in permissive mode permanently. It's there for a reason, and this is just a workaround for a policy error in KitKat. The SELinux SetEnforce Toggle app is a convenient way to turn it off and on for this.

Mount slave namespace workaround

Android apps that mount filesystems (e.g. CIFS, Lil'Debi's loopback fs), mount them in a private namespace that is not shared with other apps (as explained by mkasick). There is a rom-based workaround applied in CM-based roms, and probably many others, but not in stock. Instead, I am applying his kernel/ramdisk based workaround. If you are on stock and need this workaround, do not use the anykernel build; use the one with the full disk image.

Configurable baseband_xmm_power wakelock timeout

This is based on work by Sgt. Meow, with some tweaks. It is controlled by the module param /sys/modules/baseband_xmm_power/bb_timeout, which defaults to 10, and represents the time, in 10ths of a second, that the baseband_xmm_power wakelock should be acquired for before timing out. 0 will disable the wakelock completely as in earlier versions of carcosa-kernel. These semantics are not the same as those for the same parameter in Oxydo, so be aware.

-------------------------------------------------------------------------------------------------------
Camilla: You, sir, should unmask.
Stranger: Indeed?
Cassilda: Indeed, it's time. We all have laid aside disguise but you.
Stranger: I wear no mask.
Camilla: (Terrified, aside to Cassilda) No mask? No mask!
– from Act 1, Scene 2 of The King In Yellow

bjcrj said:

Kernel rocks! Thanks!

Click to expand...

Click to collapse

You're welcome. Are you using the milestone release or the alpha? And are you on grouper or tilapia? I want to know if the baseband_xmm_power hack is being tested by anyone besides me.

gremlin89 said:

Hi, I'm using the newest CM Release and after flashing the kernel i got a com.android.phone has stopped error. I cleared the cache and the dalvik before restart.

Click to expand...

Click to collapse

The boot.img in the zips I've provided us built with a stock ramdisk, and CM needs its own ramdisk. Perhaps I could build an AnyKernel zip for non stock users.

gremlin89 said:

Oh that would be really great. Is it easy to build such a rom?

Click to expand...

Click to collapse

Not a ROM, just an updater zip. In principle, it should be easy. But somehow, I've never got it to work.

sengst said:

Thank you very much for your work! Without your kernel my battery was empty within one or two days due to the annoying wakelocks, now my N7 runs since 7 days and I still have 40%! Awesome!

Click to expand...

Click to collapse

I'm glad to hear it. Am I correct in assuming that you have a tilapia device, and are running the alpha version of the kernel?

ispukan said:

What is the difference between Milestone and Alpha ? btw i am using nexus 7 wi-fi only model

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Click to collapse

Currently, the difference is that the alpha disables the baseband_xmm_power wakelock, which some people perceive to be a major source of idle power drain on the 3g (tilapia) model.

ispukan said:

So i can install what ever i want there is now difference for wifi only model ?

Click to expand...

Click to collapse

Right; you can run either on a Wi-Fi only (grouper) device, but the changes are only relevant to tilapia.