[Intel-gfx] [PATCH 01/12] drm/i915: Remove bogus GEM_BUG_ON in unpark

[John Harrison]

On 7/18/2022 05:15, Tvrtko Ursulin wrote:
>
> On 13/07/2022 00:31, John.C.Harrison at Intel.com wrote:
>> From: Matthew Brost <matthew.brost at intel.com>
>>
>> Remove bogus GEM_BUG_ON which compared kernel context timeline seqno to
>> seqno in memory on engine PM unpark. If a GT reset occurred these values
>> might not match as a kernel context could be skipped. This bug was
>> hidden by always switching to a kernel context on park (execlists
>> requirement).
>
> Reset of the kernel context? Under which circumstances does that happen?
As per description, the issue is with full GT reset.

>
> It is unclear if the claim is this to be a general problem or the 
> assert is only invalid with the GuC. Lack of a CI reported issue 
> suggests it is not a generic problem?
Currently it is not an issue because we always switch to the kernel 
context because that's how execlists works and the entire driver is 
fundamentally based on execlist operation. When we stop using the kernel 
context as a (non-functional) barrier when using GuC submission, then 
you would see an issue without this fix.

John.


>
> Regards,
>
> Tvrtko
>
>> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
>> ---
>>   drivers/gpu/drm/i915/gt/intel_engine_pm.c | 2 --
>>   1 file changed, 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c 
>> b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
>> index b0a4a2dbe3ee9..fb3e1599d04ec 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
>> +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
>> @@ -68,8 +68,6 @@ static int __engine_unpark(struct intel_wakeref *wf)
>>                ce->timeline->seqno,
>>                READ_ONCE(*ce->timeline->hwsp_seqno),
>>                ce->ring->emit);
>> -        GEM_BUG_ON(ce->timeline->seqno !=
>> -               READ_ONCE(*ce->timeline->hwsp_seqno));
>>       }
>>         if (engine->unpark)