Re: [PATCH] drm/i915: Double check ring is idle before declaring the GPU wedged

[Damien Lespiau <damien.lespiau@intel.com>]

On Mon, Aug 11, 2014 at 09:21:35AM +0100, Chris Wilson wrote:
> During ring initialisation, sometimes we observe, though not in
> production hardware, that the idle flag is not set even though the ring
> is empty. Double check before giving up.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Damien Lespiau <damien.lespiau@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index a0831c309eab..d72d5e0e693d 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -467,7 +467,12 @@ static bool stop_ring(struct intel_engine_cs *ring)
>  		I915_WRITE_MODE(ring, _MASKED_BIT_ENABLE(STOP_RING));
>  		if (wait_for((I915_READ_MODE(ring) & MODE_IDLE) != 0, 1000)) {
>  			DRM_ERROR("%s : timed out trying to stop ring\n", ring->name);
> -			return false;
> +			/* Sometimes we observe that the idle flag is not
> +			 * set even though the ring is empty. So double
> +			 * check before giving up.
> +			 */
> +			if (I915_READ_HEAD(ring) != I915_READ_TAIL(ring))
> +				return false;

That means we propably want to just put the user visible error message
there as well?

-- 
Damien