Re: [PATCH v2 12/22] drm/i915: Preserve SSC earlier

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On 07/15/2015 04:57 AM, Lukas Wunner wrote:
> Commit 92122789b2d6 ("drm/i915: preserve SSC if previously set v3")
> added code to intel_modeset_gem_init to override the SSC status read
> from VBT with the SSC status set by BIOS.
> 
> However, intel_modeset_gem_init is invoked *after* intel_modeset_init,
> which calls intel_setup_outputs, which *modifies* SSC status by way of
> intel_init_pch_refclk. So unlike advertised, intel_modeset_gem_init
> doesn't preserve the SSC status set by BIOS but whatever
> intel_init_pch_refclk decided on.
> 
> This is a problem on dual gpu laptops such as the MacBook Pro which
> require either a handler to switch DDC lines, or the discrete gpu
> to proxy DDC/AUX communication: Both the handler and the discrete
> gpu may initialize after the i915 driver, and consequently, an LVDS
> connector may initially seem disconnected and the SSC therefore
> is disabled by intel_init_pch_refclk, but on reprobe the connector
> may turn out to be connected and the SSC must then be enabled.
> 
> Due to 92122789b2d6 however, the SSC is not enabled on reprobe since
> it is assumed BIOS disabled it while in fact it was disabled by
> intel_init_pch_refclk.
> 
> Also, because the SSC status is preserved so late, the preserved value
> only ever gets used on resume but not on panel initialization:
> intel_modeset_init calls intel_init_display which indirectly calls
> intel_panel_use_ssc via multiple subroutines, *before* the BIOS value
> overrides the VBT value in intel_modeset_gem_init (intel_panel_use_ssc
> is the sole user of dev_priv->vbt.lvds_use_ssc).
> 
> Fix this by moving the code introduced by 92122789b2d6 from
> intel_modeset_gem_init to intel_modeset_init before the invocation
> of intel_setup_outputs and intel_init_display.
> 
> Add a DRM_DEBUG_KMS as suggested way back by Jani:
> http://lists.freedesktop.org/archives/intel-gfx/2014-June/046666.html
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
> Tested-by: Paul Hordiienko <pvt.gord@gmail.com>
>     [MBP  6,2 2010  intel ILK + nvidia GT216  pre-retina]
> Tested-by: William Brown <william@blackhats.net.au>
>     [MBP  8,2 2011  intel SNB + amd turks     pre-retina]
> Tested-by: Lukas Wunner <lukas@wunner.de>
>     [MBP  9,1 2012  intel IVB + nvidia GK107  pre-retina]
> Tested-by: Bruno Bierbaumer <bruno@bierbaumer.net>
>     [MBP 11,3 2013  intel HSW + nvidia GK107  retina -- work in progress]
> 
> Fixes: 92122789b2d6 ("drm/i915: preserve SSC if previously set v3")
> Signed-off-by: Lukas Wunner <lukas@wunner.de>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 29 ++++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index af0bcfe..6335883 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -14893,6 +14893,24 @@ void intel_modeset_init(struct drm_device *dev)
>  	if (INTEL_INFO(dev)->num_pipes == 0)
>  		return;
>  
> +	/*
> +	 * 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)) {
> +		bool bios_lvds_use_ssc = !!(I915_READ(PCH_DREF_CONTROL) &
> +					    DREF_SSC1_ENABLE);
> +
> +		if (dev_priv->vbt.lvds_use_ssc != bios_lvds_use_ssc) {
> +			DRM_DEBUG_KMS("SSC %sabled by BIOS, overriding VBT which says %sabled\n",
> +				     bios_lvds_use_ssc ? "en" : "dis",
> +				     dev_priv->vbt.lvds_use_ssc ? "en" : "dis");
> +			dev_priv->vbt.lvds_use_ssc = bios_lvds_use_ssc;
> +		}
> +	}
> +
>  	intel_init_display(dev);
>  	intel_init_audio(dev);
>  
> @@ -15446,7 +15464,6 @@ err:
>  
>  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;
>  	int ret;
> @@ -15455,16 +15472,6 @@ 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);
> 

Yeah looks good (and I'm having deja vu here; I thought I ran into the same ordering issue at one point in a report from krh, but I guess I never fixed it; didn't have test hw at the time).

Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

Thanks,
Jesse
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