Re: [PATCH] drm/i915: Check DDI max lanes after applying BXT workaround

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Jan 28, 2016 at 03:09:37PM -0800, Matt Roper wrote:
> In commit bfb9faab8 we added a workaround for some BXT BIOS that fail to
> properly initialize the DDI_A_4_LANES bit of the control register (4
> lanes is the only valid configuration on BXT since there is no DDI E to
> share with).  A recent patch added some additional checks on this
> register bit before the workaround gets applied; this breaks eDP on BXT
> in some settings.  Some minor code shuffling is all we need to restore
> the workaround.
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Fixes: 7cd87cb80 ("drm/i915: Check max number of lanes when registering DDI ports")
> Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index 75b57a8..6ac80cd 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -3288,7 +3288,6 @@ void intel_ddi_init(struct drm_device *dev, enum port port)
>  	intel_dig_port->saved_port_bits = I915_READ(DDI_BUF_CTL(port)) &
>  					  (DDI_BUF_PORT_REVERSAL |
>  					   DDI_A_4_LANES);
> -	intel_dig_port->max_lanes = max_lanes;
>  
>  	/*
>  	 * Bspec says that DDI_A_4_LANES is the only supported configuration
> @@ -3301,9 +3300,12 @@ void intel_ddi_init(struct drm_device *dev, enum port port)
>  		if (!(intel_dig_port->saved_port_bits & DDI_A_4_LANES)) {
>  			DRM_DEBUG_KMS("BXT BIOS forgot to set DDI_A_4_LANES for port A; fixing\n");
>  			intel_dig_port->saved_port_bits |= DDI_A_4_LANES;
> +			max_lanes = 4;
>  		}
>  	}
>  
> +	intel_dig_port->max_lanes = max_lanes;
> +

Oops, my bad.

Might be a bit nicer to really fixup the register value before
determining max_lanes, but since there's no port E on BXT it doesn't
really matter I suppose. So this fix should be fine as is.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  	intel_encoder->type = INTEL_OUTPUT_UNKNOWN;
>  	intel_encoder->crtc_mask = (1 << 0) | (1 << 1) | (1 << 2);
>  	intel_encoder->cloneable = 0;
> -- 
> 2.1.4

-- 
Ville Syrjälä
Intel OTC
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