[Intel-gfx] [PATCH 19/19] drm/i915: Sync against the GuC log buffer flush work item on system suspend

[Imre Deak]

On to, 2016-08-18 at 19:17 +0530, Goel, Akash wrote:
> [...]
> Thanks for the inputs. Sorry not familiar with freezable WQ semantics.
> But after looking at code, this is what I understood :-
> 1. freezable Workqueues will be frozen before the system suspend
>     callbacks are invoked for the devices.

Yes.

> 2. Any work item queued after the WQ is marked frozen will be scheduled
>     later, on resume.

Yes.

> 3. But if a work item was already present in the freezable Workqueue,
>     before it was frozen and it did not complete, then system suspend
>     itself will be aborted.

System suspend will be aborted only if any kernel thread didn't
complete within a reasonable amount of time (freeze_timeout_msecs, 20
sec by default). Otherwise already queued items will be properly
waited upon and suspend will proceed.

> 4. So if the log.flush_wq is marked as freezable, then flush of
>     work item will not be required for the system suspend case.
>     And runtime suspend case is already covered with rpm get/put
>     around register access in work item function.

Yes.

> 
> It seems there are 2 config options CONFIG_SUSPEND_FREEZER

This is set whenever system suspend is enabled.

> and
> CONFIG_FREEZER 

This is set except for one platform (powerpc), where I assume freezing
of the tasks is achieved in a different way. In any case it doesn't
matter for us.

--Imre

> which have to be enabled for all the above to happen.
> If these config options will always be enabled then probably marking
> log.flush_wq would work.
> 
> Please kindly confirm whether I understood correctly or not, accordingly 
> will proceed further.
> 
> Best regards
> Akash
> 
> 
> 
> > --Imre
> >