Quoting Lorenzo Pieralisi (2014-02-22 04:09:10)
On Sat, Feb 22, 2014 at 10:38:40AM +0000, Russell King - ARM Linux wrote:
On Wed, Feb 19, 2014 at 04:12:54PM +0000, Lorenzo Pieralisi wrote:
On Wed, Feb 19, 2014 at 01:52:09AM +0000, Sebastian Capella wrote:
+/*
- Snapshot kernel memory and reset the system.
- After resume, the hibernation snapshot is written out.
- */
+static int notrace __swsusp_arch_save_image(unsigned long unused) +{
- int ret;
- ret = swsusp_save();
- if (ret == 0)
soft_restart(virt_to_phys(cpu_resume));By the time the suspend finisher (ie this function) is run, the processor state has been saved and I think that's all you have to do, function can just return after calling swsusp_save(), unless I am missing something.
I do not understand why a soft_restart is required here. On a side note, finisher is called with irqs disabled so, since you added a function for soft restart noirq, it should be used, if needed, but I have to understand why in the first place.
It's required because you can't just return from the finisher. A normal return from the finisher will always be interpreted as an abort rather than success (because the state has to be unwound.)
This is the only way to get a zero return from cpu_suspend().
Yes, that's the only reason why this code is jumping to cpu_resume, since all it is needed is to snapshot the CPU context and by the time the finisher is called that's done. Wanted to say that soft reboot is not useful (cache flushing and resume with MMU off), but what you are saying is correct. We might be saving swsusp_save return value in a global variable and just return from the finisher, but that's horrible and given the amount of time it takes to snapshot the image to disk the cost of this soft reboot will be dwarfed by that.
I wanted to ask and clarify why the code was written like this though, given its complexity.
We could also return a constant > 1. __cpu_suspend code will replace a 0 return with 1 for paths exiting suspend, but will not change return values != 0.
cpu_suspend_abort: ldmia sp!, {r1 - r3} @ pop phys pgd, virt SP, phys resume fn teq r0, #0 moveq r0, #1 @ force non-zero value mov sp, r2 ldmfd sp!, {r4 - r11, pc}
We could take advantage of that if we wanted, but Lorenzo pointed out also that the relative benefit is very low since the cost of resuming is >> soft_restart.
I'll go with leaving the soft_restart as is unless someone feels strongly against.
Thanks!
Sebastian