[Intel-gfx] [PATCH v2] drm/i915/uc: Start preparing GuC/HuC for reset

[Daniele Ceraolo Spurio]

On 26/02/18 23:50, Chris Wilson wrote:
> Quoting Sagar Arun Kamble (2018-02-27 06:54:46)
>>
>>
>> On 2/27/2018 2:22 AM, Chris Wilson wrote:
>>> Quoting Daniele Ceraolo Spurio (2018-02-26 16:57:11)
>>>> As you said we do always reset GuC no matter the value of the modparam,
>>>> but that does not reset the doorbell HW. If we're coming out of S3 and
>>>> the state as been preserved this will cause the doorbell HW to be left
>>>> in an unclean state, which could cause spurious doorbell interrupts to
>>>> be sent to GuC, not sure how the firmware handles those. The code as
>>>> moved since last time I looked at this in detail and I think we're now
>>>> most likely going to overwrite those unclean doorbells, but there are
>>>> unlikely corner cases (preempt context failing to be created) where we
>>>> might not do so.
>>> I'm still going "wait, we can put the device into D3 and the GuC is
>>> still powered?" Something feels wrong if the GuC retains state after the
>>> HW is powered down.
>> GuC will be powered down, with RC6. Just that firmware in WOPCM can get
>> wiped off if
>> memory is reset/powered down during resume. In case of mem sleep
>> generally WOPCM stays intact and if we exit
>> RC6 on resume from sleep, firmware will be restored into GuC without
>> driver intervention.
>> But since we do full GPU reset as part of sanitize we have to load it
>> from driver again.
> 
> On resume, we don't know if we are coming from module load, resume from
> S3, resume S3+RST, resume from S4, or resume from kexec. (S3+RST, kexec
> are truly without our knowledge, the others we could feed the
> information through but RST makes that moot.) Ergo, you cannot know if
> the right fw image is loaded and aiui you should treat the state as
> undefined and always reload. Does that make sense? Is there a way you
> can query what fw is loaded and so skip instead?
> -Chris
> 

Not sure if there is already a way to query the FW version, but we could 
ask for a new H2G to be added if there isn't. However, even if the 
firmware version matches, if we can't confirm it is exactly the one we 
loaded (and not a reload of the same version) there is no guarantee that 
its internal state is what we expect. Also, we would have to stop doing 
full gpu resets around suspend/resume which I doubt it is something we want.

Daniele