Re: [Intel-gfx] [PATCH 01/15] drm/i915/hdmi: do dual mode detect only if connected

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

On Thu, Oct 13, 2022 at 10:24:54PM +0300, Ville Syrjälä wrote:
> On Thu, Oct 13, 2022 at 09:41:21PM +0300, Ville Syrjälä wrote:
> > On Tue, Oct 11, 2022 at 04:49:35PM +0300, Jani Nikula wrote:
> > > For normal connector detect, there's really no point in trying dual mode
> > > detect if the connector is disconnected. We can simplify the detect
> > > sequence by skipping it. Since intel_hdmi_dp_dual_mode_detect() is only
> > > called when EDID is present, we can drop the has_edid parameter.
> > > 
> > > The functional effect is speeding up disconnected connector detection
> > > ever so slightly, and, combined with firmware EDID, also stop logging
> > > about assuming dual mode adaptor.
> > > 
> > > It's a bit subtle, but this will also skip dual mode detect if the
> > > connector is force connected and a) there's no EDID of any kind, normal
> > > or override/firmare or b) there's EDID but it does not indicate
> > > digital. These are corner cases no matter what, and arguably forcing
> > > should not be limited by dual mode detect.
> > > 
> > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/display/intel_hdmi.c | 17 +++++++----------
> > >  1 file changed, 7 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
> > > index 93519fb23d9d..a332eaac86cd 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_hdmi.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
> > > @@ -2355,7 +2355,7 @@ intel_hdmi_unset_edid(struct drm_connector *connector)
> > >  }
> > >  
> > >  static void
> > > -intel_hdmi_dp_dual_mode_detect(struct drm_connector *connector, bool has_edid)
> > > +intel_hdmi_dp_dual_mode_detect(struct drm_connector *connector)
> > >  {
> > >  	struct drm_i915_private *dev_priv = to_i915(connector->dev);
> > >  	struct intel_hdmi *hdmi = intel_attached_hdmi(to_intel_connector(connector));
> > > @@ -2371,16 +2371,13 @@ intel_hdmi_dp_dual_mode_detect(struct drm_connector *connector, bool has_edid)
> > >  	 * CONFIG1 pin, but no such luck on our hardware.
> > >  	 *
> > >  	 * The only method left to us is to check the VBT to see
> > > -	 * if the port is a dual mode capable DP port. But let's
> > > -	 * only do that when we sucesfully read the EDID, to avoid
> > > -	 * confusing log messages about DP dual mode adaptors when
> > > -	 * there's nothing connected to the port.
> > > +	 * if the port is a dual mode capable DP port.
> > >  	 */
> > >  	if (type == DRM_DP_DUAL_MODE_UNKNOWN) {
> > >  		/* An overridden EDID imply that we want this port for testing.
> > >  		 * Make sure not to set limits for that port.
> > >  		 */
> > > -		if (has_edid && !connector->override_edid &&
> > > +		if (!connector->override_edid &&
> > >  		    intel_bios_is_port_dp_dual_mode(dev_priv, port)) {
> > >  			drm_dbg_kms(&dev_priv->drm,
> > >  				    "Assuming DP dual mode adaptor presence based on VBT\n");
> > > @@ -2435,18 +2432,18 @@ intel_hdmi_set_edid(struct drm_connector *connector)
> > >  		intel_gmbus_force_bit(i2c, false);
> > >  	}
> > >  
> > > -	intel_hdmi_dp_dual_mode_detect(connector, edid != NULL);
> > > -
> > > -	intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS, wakeref);
> > > -
> > >  	to_intel_connector(connector)->detect_edid = edid;
> > >  	if (edid && edid->input & DRM_EDID_INPUT_DIGITAL) {
> > 
> > We didn't have this digital input thing before. What happens with
> > HDMI->VGA dongles for example?
> > 
> > Hmm. This whole thing might already be broken on those. I suspect
> > I've only used my HDMI->VGA dongle on LSPCON machines, so never
> > noticed this. Need to go plug that thing into a native HDMI port...
> 
> Except I must have left it elsewhere since I can't find it here.
> So can't test right now unfortunately.
> 
> I first thought this digital check thing might be due to
> the DVI-I shenanigans in intel_crt_detect_ddc(), but that
> was added for am unspecified gen2 machine in commit f5afcd3dd0dc
> ("drm/i915/crt: Check for a analog monitor in case of DVI-I")
> so not even relevant here. And I don't think I've ever seen
> a g4x+ machine with an actual DVI-I port.

Good news everyone, I found such a board: Intel DG43GT.
Well, I didn't physically find one but I found the manual
online. And some coreboot repo even had the vbt handily
available. And yes, it does show the same DDC pins being
used for the DVI-D port and CRT port. So I guess given
that these digital checks do make some sense.

-- 
Ville Syrjälä
Intel