What exacly is HSIC wakelock and why it takes the power ? Explained.
HISC is the interface that connected the main Soc processor ( Also called Applciation Processor AP) to the modem, called CP.
It does not connect to Wifi chip (SPI 2.0/3.0/4.0 is used for that). These techology is categorized under Inter processor technology.
HSIC is uses the standard USB core library and it is a standard given by usb.org. In simple terms hsic is outer two wires of USB (for power ) stripped off.
The HSIC by itself consumes very less power and is one of the very power efficient and space efficient ways of interconnecting chips. Currently common to Qualcomm, Exynos and most of the new Soc and Modem are adopting HSIC.
For more info read here : http://www.usb.org/developers/docs/
Spec no : 10,13 and 29.
The reason you seeing too frequent wake-lock and other wake-ups is due to the fact that the HSIC interface is waken up by modem pr br some app which wants to communicate with modem (read network).
Now one might say why modem is doing that ? Answer is modem is the part of mobile which is always on (though in low power state). Its always keeps listeing to some broadcast in case there is call or sms for itself. Once in a while modem has to tell this back to RIL (the service in Andoid handling all this ). So there is wakelock being hold so long the data is sent over hsic interface. Wakelock is released after some period of inactivity.
Also one more reason is EFS sync.
EFS concept : New modem architectures doesn't support a flash storage.(Saves lot of cost to manufacturer) .So every time modem needs to store something , it wakes up hisc interface and ask the AP (Main processor) to store it for him.
I see there is a lot of concern over this L2_hsic or msm hsic wakelock or hsic_pm0 wakelock ( all are essentially same) and from most of the ROM developer trying to reduce it or at times it interfere in your debugging of apps that are draining battery.
I can say at this point that it is quite natural and its a necessary evil for smooth working of your modem (network 2g,3g,4g )subsystem. Also every vendor has there way of using the HSIC device driver in kernel so expect different results or hold time.
Now how to reduce it ?
If you debugging somthing else and hsic wakelock is interfering in your overnight battery test , put phone on airplane mode, this will reduce the wakelock time by some 90% .
Note: Removing sim will still make your modem camp to network in emergency mode, So, does not help a lot in wake-ups.
Now to reduce it when modem is active and network data is active, don't expect much optimization in this regard. As it is needed to send data, call info, sms etc. It absolutely needed to communicate to modem.
Do not waste too much time optimizing in here , changing things might effect the normal working of modem, thus network issues.
Please refer some answers here for more info as why msm ? what is l2 ?
Hit thanks if it was helpful.