Re: [PATCH] drm/i915: Don't override output type for DDI HDMI

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

On Tue, Nov 24, 2015 at 01:44:46PM +0100, Daniel Vetter wrote:
> On Fri, Nov 20, 2015 at 12:18:41PM +0100, Takashi Iwai wrote:
> > On Thu, 19 Nov 2015 17:04:20 +0100,
> > Takashi Iwai wrote:
> > > 
> > > On Thu, 19 Nov 2015 16:51:05 +0100,
> > > Daniel Vetter wrote:
> > > > 
> > > > On Thu, Nov 19, 2015 at 12:09:56PM +0100, Takashi Iwai wrote:
> > > > > Currently a DDI port may register the DP hotplug handler even though
> > > > > it's used with HDMI, and the DP HPD handler overrides the encoder
> > > > > type forcibly to DP.  This caused the inconsistency on a machine
> > > > > connected with a HDMI monitor; upon a hotplug event, the DDI port is
> > > > > suddenly switched to be handled as a DP although the same monitor is
> > > > > kept connected, and this leads to the erroneous blank output.
> > > > > 
> > > > > This patch papers over the bug by excluding the previous HDMI encoder
> > > > > type from this override.  This should be fixed more fundamentally,
> > > > > e.g. by moving the encoder type reset from the HPD or by having
> > > > > individual encoder objects for HDMI and DP.  But since the bug has
> > > > > been present for a long time (3.17), it's better to have a
> > > > > quick-n-dirty fix for now, and keep working on a cleaner fix.
> > > > > 
> > > > > Bugzilla: http://bugzilla.opensuse.org/show_bug.cgi?id=955190
> > > > > Fixes: 0e32b39ceed6 ('drm/i915: add DP 1.2 MST support (v0.7)')
> > > > > Cc: <stable@vger.kernel.org> # v3.17+
> > > > > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> > > > 
> > > > If you plug in a hmid screen (using a level-shifter adapter), then a DP
> > > > screen, does still everything work?
> > >  
> > > That was my slight concern, too, although it seems working as long as
> > > I tested several HSW machines.  Maybe better to double-check.
> > 
> > I checked again some machines, and they all seem working.
> > 
> > Actually the encoder type is set again in each detection function
> > (intel_hdmi_detect(), intel_dp_detect()) no matter with or without my
> > workaround.  The problem happens when a HPD is triggered only to DP
> > while the HDMI is kept on.  Then intel_hdmi_detect() won't be called
> > so the wrongly overridden encoder type remains.
> > 
> > Why the override is still needed in intel_dp_hpd_pulse() isn't clear
> > to me, but at least it influences on the port power domain handling.
> > And my change won't affect in this regard.
> 
> My suspicion is that we need this to reset between
> INTEL_OUTPUT_DISPLAYPORT and INTEL_OUTPUT_DP_MST.

INTEL_OUTPUT_DP_MST is the type for fake mst encoders, and those
don't have a .hpd_pulse() hook to begin with.

-- 
Ville Syrjälä
Intel OTC
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