Re: [PATCH] omapdss: extend pm notifier to handle hibernation

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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On 20/03/15 16:57, Grygorii.Strashko@linaro.org wrote:
> Hi Tomi,
> 
> On 03/20/2015 02:20 PM, Tomi Valkeinen wrote:
>> On 25/02/15 19:03, grygorii.strashko@linaro.org wrote:
>>> From: Grygorii Strashko <Grygorii.Strashko@linaro.org>
>>>
>>> Add handling of missed events in omap_dss_pm_notif which are
>>> needed to support hibernation (suspend to disk).
>>>
>>> Signed-off-by: Grygorii Strashko <Grygorii.Strashko@linaro.org>
>>> ---
>>>   drivers/video/fbdev/omap2/dss/core.c | 4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/video/fbdev/omap2/dss/core.c b/drivers/video/fbdev/omap2/dss/core.c
>>> index 6b74f73..e60976a 100644
>>> --- a/drivers/video/fbdev/omap2/dss/core.c
>>> +++ b/drivers/video/fbdev/omap2/dss/core.c
>>> @@ -178,11 +178,15 @@ static int omap_dss_pm_notif(struct notifier_block *b, unsigned long v, void *d)
>>>   	DSSDBG("pm notif %lu\n", v);
>>>   
>>>   	switch (v) {
>>> +	case PM_HIBERNATION_PREPARE:
>>>   	case PM_SUSPEND_PREPARE:
>>> +	case PM_RESTORE_PREPARE:
>>>   		DSSDBG("suspending displays\n");
>>>   		return dss_suspend_all_devices();
>>>   
>>>   	case PM_POST_SUSPEND:
>>> +	case PM_POST_HIBERNATION:
>>> +	case PM_POST_RESTORE:
>>>   		DSSDBG("resuming displays\n");
>>>   		return dss_resume_all_devices();
>>>   
>>
>> Why suspend displays when PM_RESTORE_PREPARE happens? Why resume when
>> PM_POST_RESTORE happens?
> 
> We have following sequence when system is restored from hibernation:
> - original kernel booted;
> - late_initcall_sync(software_resume);
>   - pm_notifier_call_chain(PM_RESTORE_PREPARE);
>   - freeze_processes
>   - check & read hibernation image
>   - suspend all devices (.freeze())
>   - jump to stored kernel
>   - restore devices
>   ...
> 
> So, all devices should be in frozen/suspended state when we will jump to stored kernel
> (device's state should be the same as before creating hib image).
> 
> Without this patch I can see a lot of log messages like below:

Yes, I am sure a fix is needed for hibernation. But I still don't quite
understand PM_RESTORE_PREPARE and PM_POST_RESTORE.

When we enter hibernation, there's only PM_HIBERNATION_PREPARE?

When waking from hibernation, there's first PM_RESTORE_PREPARE, where we
need to disable displays that were enabled during boot. Then either
PM_POST_HIBERNATION if all went well, or PM_POST_RESTORE if there was an
error, and in both cases we want to enable the displays?

 Tomi



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