[Intel-gfx] [PATCH v2 1/2] drm/i915/ilk: Don't attempt to register eDP if LVDS was detected

[Chris Wilson]

On Sat, Jun 18, 2016 at 12:29:24AM +0300, Imre Deak wrote:
> Atm on ILK we attempt to detect if eDP is present even if LVDS was
> already detected and an encoder for it was registered. This involves
> trying to read out the eDP EDID, which in turn needs the same power
> sequencer that LVDS uses. Poking at the VDD line at an unexpected time
> may or may not interfere with the LVDS panel, but it's probably safer to
> prevent this. Registering both an LVDS and an eDP connector would also
> present a similar problem accessing the shared PPS at any point later in
> an unexpected way.
> 
> We also need this to be able fix PPS initialization before its first use
> in the next patch. For that we want to be sure that PPS is not in use
> by LVDS.
> 
> v2:
> - Split out the PPS init fix to a separate patch. (Chris)
> - Add comment about eDP init depending on LVDS init. (Chris)
> - Make the use of the intel_encoder ptr less error prone.
> 
> CC: Ville Syrjälä <ville.syrjala at linux.intel.com>
> CC: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Imre Deak <imre.deak at intel.com>

Main worry here is what if the LVDS detection was false? (I believe that
LVDS/eDP doesn't coexist...)

I'm just wondering if calling lvds_encoder->post_disable() to force the
LVDS off in this circumstance is viable. Worst case (false eDP, real
LVDS), we lose the output on the console until a mode is restored by fbdev.
Best case (false LVDS, real eDP) we don't regress detection of eDP.

(Or knowing the internals, we could just do a save restore of LVDS
PP_CONTROL around the eDP detection.)
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre