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

From: Takashi Iwai <tiwai@suse.de>
To: Daniel Vetter <daniel@ffwll.ch>
Cc: Dave Airlie <airlied@redhat.com>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915: Don't override output type for DDI HDMI
Date: Thu, 19 Nov 2015 17:04:20 +0100	[thread overview]
Message-ID: <s5hmvua7z7f.wl-tiwai@suse.de> (raw)
In-Reply-To: <20151119155105.GI17050@phenom.ffwll.local>

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.

> We rely upon the detection code to correctly adjust the encoder type,
> otherwise the subsequent modeset will pick the wrong code (even when
> userspace asked the kernel to light up the right connector). I'm not sure
> whether this is now broken ...

I guess the only case this might matter is MST, as the encoder
override didn't exist before the MST support patch, so the non-MST
case should keep working even with this change.

thanks,

Takashi

> -Daniel
> 
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 09bdd94ca3ba..d34e64300d66 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -5153,7 +5153,8 @@ intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port, bool long_hpd)
> >  	enum intel_display_power_domain power_domain;
> >  	enum irqreturn ret = IRQ_NONE;
> >  
> > -	if (intel_dig_port->base.type != INTEL_OUTPUT_EDP)
> > +	if (intel_dig_port->base.type != INTEL_OUTPUT_EDP &&
> > +	    intel_dig_port->base.type != INTEL_OUTPUT_HDMI)
> >  		intel_dig_port->base.type = INTEL_OUTPUT_DISPLAYPORT;
> >  
> >  	if (long_hpd && intel_dig_port->base.type == INTEL_OUTPUT_EDP) {
> > -- 
> > 2.6.3
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
> 
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