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

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

On Fri, Oct 14, 2022 at 11:14:43AM +0300, Jani Nikula wrote:
> On Thu, 13 Oct 2022, Ville Syrjälä <ville.syrjala@linux.intel.com> 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.
> >
> > commit aa93d632c496 ("drm/i915: Require digital monitor
> > on HDMI ports for detect") is where this check was added,
> > but there is no actual justification for checking the
> > digital thing vs. just making sure the edid read succeeded.
> >
> > So looks to me like this check can just be removed. And
> > if we do come across some real DVI-I use cases we should
> > probably check the VBT DDC pin assignments before we go
> > assuming anything about the wiring.
> 
> Are you saying remove the "edid->input & DRM_EDID_INPUT_DIGITAL"
> altogether? Or turn this into:
> 
> 	if (edid) {
> 		if (edid->input & DRM_EDID_INPUT_DIGITAL) {
> 			intel_hdmi->has_audio = drm_detect_monitor_audio(edid);
> 			intel_hdmi->has_hdmi_sink = drm_detect_hdmi_monitor(edid);
> 		}
> 		connected = true;
> 	}
> 
> Since e.g. DP wraps the audio/hdmi detect calls in digital check.

I'm thinking they should just all go. But I guess that's a separate
topic for the most part.

-- 
Ville Syrjälä
Intel