Re: [PATCH v6] drm/msm/dp: force link training for display resolution change

[Kuogee Hsieh]

On 6/14/2022 2:59 PM, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2022-06-14 14:05:02)
> > Display resolution change is implemented through drm modeset. Older
> > modeset (resolution) has to be disabled first before newer modeset
> > (resolution) can be enabled. Display disable will turn off both
> > pixel clock and main link clock so that main link have to be
> > re-trained during display enable to have new video stream flow
> > again. At current implementation, display enable function manually
> > kicks up irq_hpd_handle which will read panel link status and start
> > link training if link status is not in sync state.
> >
> > However, there is rare case that a particular panel links status keep
> > staying in sync for some period of time after main link had been shut
> > down previously at display disabled. In this case, main link retraining
> > will not be executed by irq_hdp_handle(). Hence video stream of newer
> > display resolution will fail to be transmitted to panel due to main
> > link is not in sync between host and panel.
> >
> > This patch will bypass irq_hpd_hanle() in favor of directly call
> s/hanle/handle/
>
> > dp_ctrl_on_stream() to always perform link training in regardless of
> > main link status. So that no unexpected exception resolution change
> > failure cases will happen. Also this implementation are more efficient
> > than manual kicking off irq_hpd_handle function.
> >
> > Changes in v2:
> > -- set force_link_train flag on DP only (is_edp == false)
> >
> > Changes in v3:
> > -- revise commit  text
> > -- add Fixes tag
> >
> > Changes in v4:
> > -- revise commit  text
> >
> > Changes in v5:
> > -- fix spelling at commit text
> >
> > Changes in v6:
> > -- split dp_ctrl_on_stream() for phy test case
> > -- revise commit text for modeset
> >
> > Fixes: 62671d2ef24b ("drm/msm/dp: fixes wrong connection state caused by failure of link train")
> > Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/msm/dp/dp_ctrl.c    | 31 +++++++++++++++++++++++--------
> >   drivers/gpu/drm/msm/dp/dp_ctrl.h    |  3 ++-
> >   drivers/gpu/drm/msm/dp/dp_display.c | 13 ++++++-------
> >   3 files changed, 31 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > index af7a80c..cb9c7af 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> > @@ -1807,7 +1807,27 @@ static int dp_ctrl_link_retrain(struct dp_ctrl_private *ctrl)
> >          return dp_ctrl_setup_main_link(ctrl, &training_step);
> >   }
> >
> > -int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
> > +int dp_ctrl_on_stream_phy_test_report(struct dp_ctrl *dp_ctrl)
> > +{
> > +       int ret = 0;
> Drop assignment please.
>
> > +       struct dp_ctrl_private *ctrl;
> > +
> > +       ctrl = container_of(dp_ctrl, struct dp_ctrl_private, dp_ctrl);
> > +
> > +       ctrl->dp_ctrl.pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
> > +
> > +       ret = dp_ctrl_enable_stream_clocks(ctrl);
> > +       if (ret) {
> > +               DRM_ERROR("Failed to start pixel clocks. ret=%d\n", ret);
> > +               return ret;
> > +       }
> > +
> > +       dp_ctrl_send_phy_test_pattern(ctrl);
> None of this code needs to be run in the normal display on case?

+       ctrl->dp_ctrl.pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
+
+       ret = dp_ctrl_enable_stream_clocks(ctrl);

These two lines are also used at normal display on case (dp_ctrl_on_stream()).
I have to copy them to here to form a stand alone dp_ctrl_on_stream_phy_test_report().

> > +
> > +       return 0;
> > +}
> > +
> > +int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train)
> >   {
> >          int ret = 0;
> >          bool mainlink_ready = false;
> > @@ -1843,12 +1863,7 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
> >                  goto end;
> >          }
> >
> > -       if (ctrl->link->sink_request & DP_TEST_LINK_PHY_TEST_PATTERN) {
> > -               dp_ctrl_send_phy_test_pattern(ctrl);
> > -               return 0;
> > -       }
> > -
> > -       if (!dp_ctrl_channel_eq_ok(ctrl))
> > +       if (force_link_train || !dp_ctrl_channel_eq_ok(ctrl))
> >                  dp_ctrl_link_retrain(ctrl);
> >
> >          /* stop txing train pattern to end link training */
> > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> > index c388323..b6d25ab 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_display.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> > @@ -1688,10 +1689,12 @@ void dp_bridge_enable(struct drm_bridge *drm_bridge)
> >
> >          state =  dp_display->hpd_state;
> >
> > -       if (state == ST_DISPLAY_OFF)
> > +       if (state == ST_DISPLAY_OFF) {
> >                  dp_display_host_phy_init(dp_display);
> > +               force_link_train = true;
> > +       }
> >
> > -       dp_display_enable(dp_display, 0);
> > +       dp_display_enable(dp_display, force_link_train);
> Do we need to pass it from here? Why can't dp_display_enable() simply
> check for 'state == ST_DISPLAY_OFF' and then force retrain the link?