Re: [PATCH 1/2] Revert "drm/i915: Avoid waking the engines just to check if they are idle"

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

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

> This reverts commit 0b702dca26580e3bbfbbaf22dfc29280b6263414.
>
> CI reports that this is not as reliable as it first appears, with
> failures starting to sporadically occur in selftests.
>
> Fixes: 0b702dca2658 ("drm/i915: Avoid waking the engines just to check if they are idle")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/intel_engine_cs.c | 17 ++++++-----------
>  1 file changed, 6 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> index 4f244019560d..b7b626195eda 100644
> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> @@ -968,7 +968,6 @@ static bool ring_is_idle(struct intel_engine_cs *engine)
>  {
>  	struct drm_i915_private *dev_priv = engine->i915;
>  	intel_wakeref_t wakeref;
> -	unsigned long flags;
>  	bool idle = true;
>  
>  	if (I915_SELFTEST_ONLY(!engine->mmio_base))
> @@ -979,19 +978,15 @@ static bool ring_is_idle(struct intel_engine_cs *engine)
>  	if (!wakeref)
>  		return true;
>  
> -	spin_lock_irqsave(&dev_priv->uncore.lock, flags);
> +	/* 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;
>  
> -	/*
> -	 * Check that no commands are left in the ring.
> -	 *
> -	 * If the engine is not awake, both reads return 0 as we do so without
> -	 * forcewake.
> -	 */
> -	if ((I915_READ_FW(RING_HEAD(engine->mmio_base)) & HEAD_ADDR) !=
> -	    (I915_READ_FW(RING_TAIL(engine->mmio_base)) & TAIL_ADDR))
> +	/* 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;
>  
> -	spin_unlock_irqrestore(&dev_priv->uncore.lock, flags);
>  	intel_runtime_pm_put(dev_priv, wakeref);
>  
>  	return idle;
> -- 
> 2.20.1
>
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