Re: [RFC PATCH v1 1/1] ACPI: PM: s2idle: Add lps0_screen_off sysfs interface

[Mario Limonciello <superm1@kernel.org>]

>> I will reply to the earlier reply from Rafael with more context, but
>> runtime suspend of the GPU is not part of or related to these
>> notifications.
> 
> Of course it isn't.
> 
> What we were talking about was how to get from the "displays off, no
> GUI activity" user space smoothly into system suspend and back.
> 
> You are saying that this has been done already on AMD, so I'm not sure
> why you want more.
> 

I'm not aware this existing in any unique way for AMD.  The decision of 
displays off; start a timer and enter suspend would be the same for any 
vendor.

But GPUs aren't only used for display.  If you're actively running a 
different workload (for example an LLM) using the GPU and happen to turn 
off all the displays you wouldn't want it to suspend.

What you would want is to key off:

1) All displays are off.
2) All GPUs are unsused.
3) Some time has passed.

I feel that if userspace is going to adopt a policy like this kernel 
drivers need to use runtime PM when displays are off and the GPUs aren't 
being used for anything else.

At least for AMD this doesn't happen today and would require driver 
work.  But the same kind of work would be needed by any GPU driver.