Re: [PATCH] drm/i915: Don't load context at driver init time on SNB

[Ben Widawsky <ben@bwidawsk.net>]

On Fri, Aug 09, 2013 at 08:32:54PM -0700, Stéphane Marchesin wrote:
> This is a partial revert of b4ae3f22d238617ca11610b29fde16cf8c0bc6e0
> (drm/i915: load boot context at driver init time)
> 
> This bit breaks hardware video decode for me after resume.
> 
> Signed-off-by: Stéphane Marchesin <marcheu@chromium.org>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index f895d15..ffa4ab2 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4614,10 +4614,6 @@ static void gen6_init_clock_gating(struct drm_device *dev)
>  		   ILK_DPARBUNIT_CLOCK_GATE_ENABLE  |
>  		   ILK_DPFDUNIT_CLOCK_GATE_ENABLE);
>  
> -	/* WaMbcDriverBootEnable:snb */
> -	I915_WRITE(GEN6_MBCTL, I915_READ(GEN6_MBCTL) |
> -		   GEN6_MBCTL_ENABLE_BOOT_FETCH);
> -
>  	g4x_disable_trickle_feed(dev);
>  
>  	/* The default value should be 0x200 according to docs, but the two

I was looking at this a bit with Stéphane. One thing we both see is that
the bit isn't sticking as it should. Clearly doing the write is having
an effect, but something is seriously wrong. Writing the bit manually
with IGT does make the bit stick.

Stéphane, could you try to write the bit with IGT before and after
resume, and see if it helps?

Adding Jesse to the CC, since he wrote the original patch, maybe he has
an idea why it doesn't stick.

-- 
Ben Widawsky, Intel Open Source Technology Center
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