[PATCH] drm/msm/dp: support setting the DP subconnector type

[Stephen Boyd]

Quoting Dmitry Baryshkov (2023-09-07 14:48:54)
> On 08/09/2023 00:34, Stephen Boyd wrote:
> > Quoting Dmitry Baryshkov (2023-09-03 15:24:32)
> >> diff --git a/drivers/gpu/drm/msm/dp/dp_panel.c b/drivers/gpu/drm/msm/dp/dp_panel.c
> >> index 97ba41593820..1cb54f26f5aa 100644
> >> --- a/drivers/gpu/drm/msm/dp/dp_panel.c
> >> +++ b/drivers/gpu/drm/msm/dp/dp_panel.c
> >> @@ -162,6 +162,11 @@ int dp_panel_read_sink_caps(struct dp_panel *dp_panel,
> >>                  }
> >>          }
> >>
> >> +       rc = drm_dp_read_downstream_info(panel->aux, dp_panel->dpcd,
> >> +                                        dp_panel->downstream_ports);
> >> +       if (rc)
> >> +               return rc;
> >
> > I haven't been able to test it yet, but I think with an apple dongle
> > we'll never populate the 'downstream_ports' member if the HDMI cable is
> > not connected when this runs. That's because this function bails out
> > early before trying to read the downstream ports when there isn't a
> > sink. Perhaps we need to read it again when an hpd_irq comes in, or we
> > need to read it before bailing out from here?
>
> I don't have an Apple dongle here. But I'll run a check with first
> connecting the dongle and plugging the HDMI afterwards.
>
> However my expectation based on my previous tests is that we only get
> here when the actual display is connected.
>

We get here when HPD is high. With an apple dongle, hpd is high when
just the dongle is plugged in. That calls dp_display_process_hpd_high()
which calls dp_panel_read_sink_caps(), but that returns with an error
(-ENOTCONN) and then we wait for something to change. When the HDMI
cable is plugged in (i.e. an actual display) we get an irq_hpd. That
causes dp_irq_hpd_handle() to call dp_display_usbpd_attention_cb() which
calls dp_link_process_request() that sees 'sink_request &
DS_PORT_STATUS_CHANGED' and thus calls
dp_display_handle_port_ststus_changed() (that has a typo right?) which
hits the else condition and calls dp_display_process_hpd_high().

So yes? We will eventually call dp_panel_read_sink_caps() again, and
this time not bail out early. It's probably fine.