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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 13/07/2022 00:31, John.C.Harrison@Intel.com wrote:
> From: Matthew Brost <matthew.brost@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?

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?

Regards,

Tvrtko

> Signed-off-by: Matthew Brost <matthew.brost@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)