[Intel-gfx] [PATCH] drm/i915: Keep engine alive as we retire the context

[Chris Wilson]

Quoting Chris Wilson (2019-06-17 09:40:44)
> Though we pin the context first before taking the pm wakeref, during
> retire we need to unpin before dropping the pm wakeref (breaking the
> "natural" onion). During the unpin, we may need to attach a cleanup
> operation on to the engine wakeref, ergo we want to keep the engine
> awake until after the unpin.
> 
> Fixes: ce476c80b8bf ("drm/i915: Keep contexts pinned until after the next kernel context switch")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/i915_request.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index 9819483d1b5d..8d952bc03d5c 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -250,8 +250,9 @@ static bool i915_request_retire(struct i915_request *rq)
>  
>         local_irq_enable();
>  
> -       intel_context_exit(rq->hw_context);
> +       /* Onion reversed to keep engine alive until after unpinning */
>         intel_context_unpin(rq->hw_context);
> +       intel_context_exit(rq->hw_context);

The alternative is to keep the onion unwind here and to add the engine
wakerefs into the barriers. Hmm.

That seems like it should be more foolproof, perhaps?
-Chris