Re: [PATCH 1/5] drm/i915: kicking rings stuck on semaphores considered harmful

[Ben Widawsky <ben@bwidawsk.net>]

On Sun, 30 Oct 2011 20:12:08 +0100
Daniel Vetter <daniel.vetter@ffwll.ch> wrote:

> If our semaphore logic gets confused and we have a ring stuck waiting
> for one, there's a decent chance it'll just execute garbage when being
> kicked. Also, kicking the ring obscures the place where the error
> first occured, making error_state decoding much harder.
> 
> So drop this an let gpu reset handle this mess in a clean fashion.
> 
> In contrast, kicking rings stuck on MI_WAIT is rather harmless, at
> worst there'll be a bit of screen-flickering. There's also old
> broken userspace out there which needs this as a  work-around.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Reviewed-by: Chris Wilson <chris@hchris-wilson.co.uk>
> Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/i915_irq.c |    7 -------
>  1 files changed, 0 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index b40004b..69d4044 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -1649,13 +1649,6 @@ static bool kick_ring(struct intel_ring_buffer *ring)
>  		I915_WRITE_CTL(ring, tmp);
>  		return true;
>  	}
> -	if (IS_GEN6(dev) &&
> -	    (tmp & RING_WAIT_SEMAPHORE)) {
> -		DRM_ERROR("Kicking stuck semaphore on %s\n",
> -			  ring->name);
> -		I915_WRITE_CTL(ring, tmp);
> -		return true;
> -	}
>  	return false;
>  }
>  

This also has the added benefit that it fixes a forcewake race on gen6+.
Ben