Re: [PATCH 3/3] drm/i915: Check the ring is empty when declaring the engines are idle

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> As another precaution when testing whether the CS engine is actually
> idle, also inspect the ring's HEAD/TAIL registers, which should be equal
> when there are no commands left to execute by the GPU.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_engine_cs.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> index 699f2d3861c7..bc38bd128b76 100644
> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> @@ -1212,6 +1212,11 @@ static bool ring_is_idle(struct intel_engine_cs *engine)
>  
>  	intel_runtime_pm_get(dev_priv);
>  
> +	/* First check that no commands are left in the ring */
> +	if ((I915_READ_HEAD(engine) & HEAD_ADDR) !=
> +	    (I915_READ_TAIL(engine) & TAIL_ADDR))
> +		idle = false;
> +

You are already certain that is not idle so why not goto out?
-Mika

>  	/* No bit for gen2, so assume the CS parser is idle */
>  	if (INTEL_GEN(dev_priv) > 2 && !(I915_READ_MODE(engine) & MODE_IDLE))
>  		idle = false;
> -- 
> 2.11.0
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