[Intel-gfx] [PATCH 1/4] drm/i915: preserve SSC if previously set v3

[Jani Nikula]

On Thu, 09 Oct 2014, Jesse Barnes <jbarnes at virtuousgeek.org> 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.
>
> v2: honor modparam if set too (Daniel)
>     read out at init time and store for panel_use_ssc() use (Jesse)
> v3: trust BIOS configuration over VBT like we do for DP (Jani)
>
> Reported-by: Kristian Høgsberg <hoegsberg at gmail.com>
> Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>

Reviewed-by: Jani Nikula <jani.nikula at intel.com>

In the long run I'd like to restrict changing dev_priv->vbt within
intel_bios.c only, regardless of whether that info comes from VBT or
what was set by the BIOS. We have a few exceptions here and there now,
and there's not a good place to plug this one in, really.


BR,
Jani.


> ---
>  drivers/gpu/drm/i915/intel_display.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 1363a93..3823135 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -13333,6 +13333,7 @@ void intel_modeset_setup_hw_state(struct drm_device *dev,
>  
>  void intel_modeset_gem_init(struct drm_device *dev)
>  {
> +	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct drm_crtc *c;
>  	struct drm_i915_gem_object *obj;
>  
> @@ -13340,6 +13341,16 @@ void intel_modeset_gem_init(struct drm_device *dev)
>  	intel_init_gt_powersave(dev);
>  	mutex_unlock(&dev->struct_mutex);
>  
> +	/*
> +	 * There may be no VBT; and if the BIOS enabled SSC we can
> +	 * just keep using it to avoid unnecessary flicker.  Whereas if the
> +	 * BIOS isn't using it, don't assume it will work even if the VBT
> +	 * indicates as much.
> +	 */
> +	if (HAS_PCH_IBX(dev) || HAS_PCH_CPT(dev))
> +		dev_priv->vbt.lvds_use_ssc = !!(I915_READ(PCH_DREF_CONTROL) &
> +						DREF_SSC1_ENABLE);
> +
>  	intel_modeset_init_hw(dev);
>  
>  	intel_setup_overlay(dev);
> -- 
> 1.9.1
>
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-- 
Jani Nikula, Intel Open Source Technology Center