[Intel-gfx] [PATCH] drm/i915: Reject modeset when the same digital port is used more than once

[Ville Syrjälä]

On Mon, May 19, 2014 at 04:29:57PM +0200, Daniel Vetter wrote:
> On Mon, May 19, 2014 at 05:19:09PM +0300, ville.syrjala at linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > On pre-HSW we have two encoders per digital port: one HDMI, one DP.
> > However they are the same physical port in hardware and we can't enable
> > both at the same time. Reject the modeset if the user attempts this.
> > 
> > So far we've been saved by the fact that we never see both HDMI and DP
> > connectors as connected. But if the user decides to force a mode anyway,
> > all kinds of funny stuff might happen.
> > 
> > Unfortunately we don't seem to have any way to inform userspace that
> > such configurations are invalid except by returning an error from
> > setcrtc. possible_clones only covers real cloning situations, and
> > looking at the connector names doesn't work either since we don't
> > always register both connectors for the same port. I suppose the
> > only way to fix that would be to expose only a single encoder per
> > digital port like we do on HSW+ but that would be a fairly large
> > undertaking for little gain.
> > 
> > kms_setmode hits this since it forces modes on non-connected VGA and
> > HDMI connectors. Previosuly it just resulted in weirdness such as
> > failed link training. With this patch it will now get an error back
> > from the kernel and will die with an assert since it thinks that the
> > configuration should be fine.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Do we have a bugzilla for this somewhere?

No idea. Can't spot anything right now that would match my IVB
kms_setmode symptoms (tons of link training failures when the same port
gets used for both DP and HDMI).

-- 
Ville Syrjälä
Intel OTC