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

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 24 Nov 2015, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Tue, Nov 24, 2015 at 03:08:17PM +0200, Ville Syrjälä wrote:
>> 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.
>
> Hm ... that would mean we only need this for the initial hotplug when we
> go _UNKOWN -> _DISPLAYPORT. Oh well, putting it into the state properly,
> derived from what userspace wants, should be the proper fix anyway. But
> for stable this is good enough.


Pushed to drm-intel-fixes, thanks for the patch and review.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center
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