[Intel-gfx] [PATCH 2/2] drm/i915: Extend hotplug detect retry on TypeC connectors to 5 seconds

[Imre Deak]

On Wed, Apr 01, 2020 at 04:50:23PM +0530, Anshuman Gupta wrote:
> On 2020-03-30 at 15:24:25 +0530, Imre Deak wrote:
> > On TypeC ports if a sink deasserts/reasserts its HPD signal, generating
> > a hotplug interrupt without the sink getting unplugged/replugged from
> > the connector, there can be an up to 3 seconds delay until the AUX
> > channel gets functional. To avoid detection failures this delay causes
> > retry the detection for 5 seconds.
> > 
> > I noticed this on ICL/TGL RVPs and a DELL XPS 13 7390 ICL laptop.
> > 
> > References: https://gitlab.freedesktop.org/drm/intel/issues/1067
> > Signed-off-by: Imre Deak <imre.deak at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_ddi.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> > index 4f508bf70f3b..2d947ff83488 100644
> > --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> > +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> > @@ -4371,7 +4371,10 @@ static enum intel_hotplug_state
> >  intel_ddi_hotplug(struct intel_encoder *encoder,
> >  		  struct intel_connector *connector)
> >  {
> > +	struct drm_i915_private *i915 = to_i915(encoder->base.dev);
> >  	struct intel_digital_port *dig_port = enc_to_dig_port(encoder);
> > +	enum phy phy = intel_port_to_phy(i915, encoder->port);
> > +	bool is_tc = intel_phy_is_tc(i915, phy);
> >  	struct drm_modeset_acquire_ctx ctx;
> >  	enum intel_hotplug_state state;
> >  	int ret;
> > @@ -4414,8 +4417,15 @@ intel_ddi_hotplug(struct intel_encoder *encoder,
> >  	 * valid EDID. To solve this schedule another detection cycle if this
> >  	 * time around we didn't detect any change in the sink's connection
> >  	 * status.
> > +	 *
> > +	 * Type-c connectors which get their HPD signal deasserted then
> > +	 * reasserted, without unplugging/replugging the sink from the
> > +	 * connector, introduce a delay until the AUX channel communication
> > +	 * becomes functional. Retry the detection for 5 seconds on type-c
> > +	 * connectors to account for this delay.
> >  	 */
> > -	if (state == INTEL_HOTPLUG_UNCHANGED && !connector->hotplug_retries &&
> > +	if (state == INTEL_HOTPLUG_UNCHANGED &&
> > +	    connector->hotplug_retries < (is_tc ? 5 : 1) &&
>
> I had observed that intel_dp_detect may race between user spece
> invoked get connector call and intel_encoder_hotplug(), that may leave
> connector status to be UNCHANGED in actual hotplug flow as
> intel_dp_detect() already called from
> drm_helper_probe_single_connector_modes(), this may results in 5
> retries for type-C ports for normal HPD assertion.  Please correct me
> if i am wrong.

Yes, it's possible the retries will be unneccessary, but I don't think
we can do much about avoiding a race between a hotplug event and a
detect call.

> Thanks,
> Anshuman Gupta.
> >  	    !dig_port->dp.is_mst)
> >  		state = INTEL_HOTPLUG_RETRY;
> >  
> > -- 
> > 2.23.1
> > 
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