[Intel-gfx] [PATCH 5/8] drm/i915: preserve SSC if previously set

[Daniel Vetter]

On Fri, Mar 07, 2014 at 08:57:52AM -0800, Jesse Barnes wrote:
> Some machines may have a broken VBT or no VBT at all, but we still want
> to use SSC there.  So check for it and keep it enabled if we see it
> already on.  Based on an earlier fix from Kristian.
> 
> Reported-by: Kristian Høgsberg <hoegsberg at gmail.com>
> Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 479de3b..d450ab6 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -5806,6 +5806,10 @@ static void ironlake_init_pch_refclk(struct drm_device *dev)
>  	 */
>  	val = I915_READ(PCH_DREF_CONTROL);
>  
> +	/* Preserve SSC if the BIOS set it */
> +	if (val & DREF_SSC1_ENABLE)
> +		i915.panel_use_ssc = 1;

This definitely needs some debug output, and we need to make sure that the
module option still overrides this.
-Daniel

> +
>  	/* As we must carefully and slowly disable/enable each source in turn,
>  	 * compute the final state we want first and check if we need to
>  	 * make any changes at all.
> -- 
> 1.8.4.2
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch