[Intel-gfx] [PATCH] drm/i915/cnl: DDIA Lane capability bit not set in clone mode

[Ville Syrjälä]

On Tue, Oct 17, 2017 at 09:27:39AM -0700, Rodrigo Vivi wrote:
> On Tue, Oct 17, 2017 at 12:10:16PM +0000, Ville Syrjälä wrote:
> > On Mon, Oct 16, 2017 at 04:44:49PM -0700, Rodrigo Vivi wrote:
> > > From: Clint Taylor <clinton.a.taylor at intel.com>
> > > 
> > > DDIA Lane capability control 4 lane bit is not being set by firmware during
> > > clone mode boot. This occurs when multiple monitors are connected during
> > > boot. The driver will configure the port for 2 lane maximum width if this
> > > bit is not set.
> > > 
> > > Cc: Mika Kahola <mika.kahola at intel.com>
> > > Signed-off-by: Clint Taylor <clinton.a.taylor at intel.com>
> > > Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_ddi.c | 5 +++--
> > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> > > index a9c0c16e3838..0ad915d71132 100644
> > > --- a/drivers/gpu/drm/i915/intel_ddi.c
> > > +++ b/drivers/gpu/drm/i915/intel_ddi.c
> > > @@ -2791,9 +2791,10 @@ void intel_ddi_init(struct drm_i915_private *dev_priv, enum port port)
> > >  	 * configuration so that we use the proper lane count for our
> > >  	 * calculations.
> > >  	 */
> > > -	if (IS_GEN9_LP(dev_priv) && port == PORT_A) {
> > > +	if ((IS_GEN9_LP(dev_priv) || IS_CANNONLAKE(dev_priv)) &&
> > > +	    port == PORT_A) {
> > >  		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");
> > > +			DRM_DEBUG_KMS("BIOS forgot to set DDI_A_4_LANES for port A\n");
> > >  			intel_dig_port->saved_port_bits |= DDI_A_4_LANES;
> > >  			max_lanes = 4;
> > >  		}
> > 
> > CNL has DDI E so this doesn't make sense. If there are CNLs out there
> > that don't actually use DDI E but forget to configure the bifurcation
> > coreectly, then we'll need a fancier way to detect that. Ie. we need to
> > be sure DDI E isn't going to be used before we can force DDI A to use
> > 4 lanes.
> 
> We got the confirmation that DDI E is not there for any of the current SKUs
> what support is currently merged.
> 
> DDI E is only available on the SKUs that posted yesterday... the one that
> supports DDI F that is the proper split. Also when DDI F is in use DDI E
> cannot be used because the interrupts handling.
> 
> So apparently this is not going to be used at all. But I agree that it
> would be good if we could have a smarter way to detect it... Any idea?

Looks like DDI E doesn't have a hardware strap, so I suppose you could
just check vbt.ddi_port_info. That still doesn't protect us against
accidentally using 4 lanes when we should have used 2. Not sure there's
anything in VBT that could help us there.

-- 
Ville Syrjälä
Intel OTC