[Intel-gfx] [PATCH 08/12] drm/i915/guc: Wait for doorbell to be inactive before deallocating

[Oscar Mateo]

On 03/21/2017 11:20 AM, Ceraolo Spurio, Daniele wrote:
>
>
> On 3/21/2017 2:02 AM, Oscar Mateo wrote:
>> Doorbell release flow requires that we wait for GEN8_DRB_VALID bit to go
>> to zero after updating db_status before we call the GuC to release the
>> doorbell.
>>
>> Kudos to Daniele for finding this out.
>>
>> v2: WARN instead of DRM_ERROR (Joonas)
>>
>> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
>> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
>> Signed-off-by: Oscar Mateo <oscar.mateo at intel.com>
>
> Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
>
> I'd like Joonas to give his ack on not returning after the wait since 
> he commented on it in the previous version. I personally prefer it 
> this way because we gain a bit more time for the doorbell to disable 
> itself (there is no spec in regards to how long this should take, but 
> it should be quick) while the GuC processes the H2G. If we ever see a 
> case where the warn fires but the H2G is successful it would mean that 
> we have to tune our wait time.
>
> Thanks,
> Daniele

True. I went with his second option (WARN instead of DRM_ERROR) without 
asking him first...

Thanks,
-- Oscar