From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Wilson <chris@chris-wilson.co.uk>
Subject: Re: [PATCH 1/2] drm/i915: time out of load detect
	busy-waits
Date: Wed, 25 Apr 2012 18:14:37 +0100
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References: <1334948616-16073-1-git-send-email-daniel.vetter@ffwll.ch>
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Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
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On Fri, 20 Apr 2012 21:03:35 +0200, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> If we try to do that and the scanlines just wouldn't advance, we
> busy-hang the machine holding the modeset mutex. Not great for
> debugging.
> 
> References: https://bugzilla.kernel.org/show_bug.cgi?id=43020
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Reviewer hangs head in shame:

> +		if (wait_for(I915_READ(pipe_dsl_reg) >= vactive, 1000))
> +			DRM_ERROR("timed out waiting for vactive in "
> +				  "load_detect, scanline: %u\n",
> +				  I915_READ(pipe_dsl_reg));
> +		if (wait_for((dsl = I915_READ(pipe_dsl_reg)) <= vsample, 1000))
> +			DRM_ERROR("timed out waiting for vsample in "
> +				  "load_detect, scanline: %u\n",
> +				  I915_READ(pipe_dsl_reg));

wait_for() catches us out everytime we convert and existing while(),
because the predicate is when it stops. Perhaps if we had a wait_until,
but anyway the fix here is:

if (wait_for(I915_READ(pipe_dsl_reg) < vactive, 1000))
  ...
if (wait_for((dsl = I915_READ(pipe_dsl_reg)) > vsample, 1000))
  ...
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre