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

[Matt Roper <matthew.d.roper@intel.com>]

On Fri, Jan 29, 2016 at 04:49:29PM +0200, Ville Syrjälä wrote:
> 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>

Pushed to dinq; thanks for the review.


Matt

> 
> >  	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

-- 
Matt Roper
Graphics Software Engineer
IoTG Platform Enabling & Development
Intel Corporation
(916) 356-2795
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