implementing "suspend to ram" on cortex A8 based on linux 3.0.8

yang gqyang hustgqyang at gmail.com
Wed Mar 7 15:05:18 UTC 2012


dear all:
I am working on arm cortex a8 now, trying to implement "suspend to ram"
based on linux 3.0.8.
Before i start my work, the soc already support standby(the cpu is on wfi
state), so in order to implement "suspend to ram", i think i just need to
implement the arch-specific related api. The "suspend to ram" works like
this:
"echo mem > /sys/power/state"  -> enter_state -> suspend_devices_and_enter
->suspend_ops->enter(state)
 Is that right? Do you think the "suspend to ram" can be realized in this
way?
In order to power off the cortex A8, i save all the writable co-processor
and   all modes's state register set, and restore them when resuming.
All the code seems work ok, because when I just does not power off the
cortex-A8 and jump to excute the resume code, the system works well. But,
when I power off the cpu, and wake up and excute resume code, the kernel
seem ok, but the busybox toolkit does not work proper, eg: "ls" can not
output the result through serial port. i add "printk statement" trying to
locate the reason, but at this time, the "ls" work fine.  hence, i doubt
something must be corrupted after resume.
I have checked all the state register and co-processor, having not found
any exception, and I also compared all the dram data before power off and
after wake up, nothing have changed. Right now, I do not know what has
happened, and what should I do to locate the real problem to make the
busybox works ok. I also want to know does the linux kernel 3.0.8 support
"suspend to ram" like this:
"echo mem > /sys/power/state"  -> enter_state -> suspend_devices_and_enter
->suspend_ops->enter(state)?
Can anyone give me some suggestion? Any comment is welcome, thanks a lot.

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