[Intel-gfx] [PATCH] drm/i915: Show stack (by WARN) for hitting forcewake errors

[Tvrtko Ursulin]

On 20/07/2018 12:11, Chris Wilson wrote:
> On Sandybridge, we need a workaround to wait for the CPU thread to wake
> up before we are sure that we have enabled the GT power well. However,
> we do see the errors being reported and failed reads returning spurious
> results. To try and capture more details as it fails, promote the error
> into a WARN so we grab the stacktrace, and to try and reduce the
> frequency of error increase the timeout from 500us to 5ms.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/intel_uncore.c | 18 ++++++++++++++----
>   1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index b892ca8396e8..284be151f645 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -283,14 +283,24 @@ fw_domains_reset(struct drm_i915_private *i915,
>   		fw_domain_reset(i915, d);
>   }
>   
> +static inline u32 gt_thread_status(struct drm_i915_private *dev_priv)
> +{
> +	u32 val;
> +
> +	val = __raw_i915_read32(dev_priv, GEN6_GT_THREAD_STATUS_REG);
> +	val &= GEN6_GT_THREAD_STATUS_CORE_MASK;
> +
> +	return val;
> +}
> +
>   static void __gen6_gt_wait_for_thread_c0(struct drm_i915_private *dev_priv)
>   {
> -	/* w/a for a sporadic read returning 0 by waiting for the GT
> +	/*
> +	 * w/a for a sporadic read returning 0 by waiting for the GT
>   	 * thread to wake up.
>   	 */
> -	if (wait_for_atomic_us((__raw_i915_read32(dev_priv, GEN6_GT_THREAD_STATUS_REG) &
> -				GEN6_GT_THREAD_STATUS_CORE_MASK) == 0, 500))
> -		DRM_ERROR("GT thread status wait timed out\n");
> +	WARN_ONCE(wait_for_atomic_us(gt_thread_status(dev_priv) == 0, 5000),
> +		  "GT thread status wait timed out\n");
>   }
>   
>   static void fw_domains_get_with_thread_status(struct drm_i915_private *dev_priv,
> 

Quite a large increase - but I guess nothing we can do if it's hit, nor 
it's better to time out faster if the wait needs to be longer.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Regards,

Tvrtko