[Intel-gfx] [PATCH] drm/i915: Sanitize PCH port transcoder select on IBX

[Chris Wilson]

Quoting Ville Syrjala (2018-11-08 14:36:35)
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> IBX has a documented workaround which states that when we disable the
> port we must change its transcoder select to A, otherwise it will
> prevent the other port (DP vs. HDMI/SDVO) from using transcoder A.
> We implement the workaround during encoder disable, but looks like
> some BIOSen leave transcoder B selected even when the port wasn't
> actually enabled by the BIOS. That will trip up our asserts
> that attempt to make sure we never forget this w/a.
> 
> Sanitize the transcoder select to A for all disabled PCH
> DP/HDMI/SDVO ports. We assume that the port was never enabled
> by the BIOS on transcoder B, because if it had we'd actually have
> to toggle the port on and back off to properly switch it back to
> transcoder A. That would cause some display flicker if transcoder A
> is already enabled on some other port, so it's better not to do it
> unless absolutely necessary. Since we have no indication that the
> transcoder select is misbehaving on the affected machines we can
> assume the port was never actually enabled by the BIOS.
> 
> This cures warning like this during driver load:
> IBX PCH DP C still using transcoder B
> WARNING: CPU: 2 PID: 172 at drivers/gpu/drm/i915/intel_display.c:1279 assert_pch_dp_disabled+0x9e/0xb0 [i915]
> 
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 61 ++++++++++++++++++++++++++++
>  1 file changed, 61 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index ae6d58dbf1ed..71b7bff85e52 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -15653,6 +15653,64 @@ static void intel_early_display_was(struct drm_i915_private *dev_priv)
>         }
>  }
>  
> +static void ibx_sanitize_pch_hdmi_port(struct drm_i915_private *dev_priv,
> +                                      enum port port, i915_reg_t hdmi_reg)
> +{
> +       u32 val = I915_READ(hdmi_reg);
> +
> +       if (val & SDVO_ENABLE ||
> +           (val & SDVO_PIPE_SEL_MASK) == SDVO_PIPE_SEL(PIPE_A))
> +               return;

Hmm, the w/a is also applied in intel_sdvo.c. Do we need to worry about
those as well?

Oh my, it's perfectly obvious SDVO is aliased to HDMI on ibx.

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

I would have s/hdmi/svdo/ here so that the labelling was all consistent
and added a reminder in the comment below that hdmi is aliased to sdvo.
-Chris