Re: [PATCH] drm/i915: Fail gpu reset if the forcewake fifo hasn't drained

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Mar 07, 2014 at 09:09:03PM +0100, Daniel Vetter wrote:
> Since the gpu reset + full ppgtt merge we have a hard hang on snb when
> running the gem_reset_stat tests. Recently Mika also some more strict
> forcewake fifo warnigns for gen6/7 in
> 
> commit 20277c60ed08ab4f7237854cc6c2046649f9200f
> Author: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Date:   Wed Mar 5 18:08:19 2014 +0200
> 
>     drm/i915: Always set fifo count to zero in gen6_reset
> 
> and they _do_ fire just right before the the final failing reset which
> then results in the machine's ultimate demise.
> 
> So use this indicator to fail the gpu reset with an -EIO code,
> preventing further command submission, further hangs and so the deadly
> final gpu reset attempt. It seems to work and my snb survives now.
> 
> The gpu is still dead though unfortunately.
> 
> Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=74100
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/intel_uncore.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index c666af8232ef..9e22b11d0b0c 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -989,9 +989,11 @@ static int gen6_do_reset(struct drm_device *dev)
>  	if (fw_engine)
>  		dev_priv->uncore.funcs.force_wake_get(dev_priv, fw_engine);
>  
> -	if (IS_GEN6(dev) || IS_GEN7(dev))
> -		WARN_ON((__raw_i915_read32(dev_priv, GTFIFOCTL) &
> -			 GT_FIFO_FREE_ENTRIES_MASK) != 0);
> +	if (IS_GEN6(dev) || IS_GEN7(dev)) {
> +		if (WARN_ON((__raw_i915_read32(dev_priv, GTFIFOCTL) &
> +			     GT_FIFO_FREE_ENTRIES_MASK) != 0))
> +		    ret = -EIO;

Chris pointed out that this WARN doesn't make much sense, and testing
confirmed that this completely breaks gpu reset on my machines here.

I've backed out Mika's original patch, this seems to be the wrong path.
-Daniel

> +	}
>  
>  	dev_priv->uncore.fifo_count = 0;
>  
> -- 
> 1.8.1.4
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch