Re: [PATCH v2] drm/msm/dp: stop event kernel thread when DP unbind

[Kuogee Hsieh]

On 4/13/2022 4:19 PM, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2022-04-13 14:04:25)
> > Current DP driver implementation, event thread is kept running
> > after DP display is unbind. This patch fix this problem by disabling
> > DP irq and stop event thread to exit gracefully at dp_display_unbind().
> >
> > Changes in v2:
> > -- start event thread at dp_display_bind()
> >
> > Fixes: e91e3065a806 ("drm/msm/dp: Add DP compliance tests on Snapdragon Chipsets")
> > Signed-off-by: Kuogee Hsieh <quic_khsieh@xxxxxxxxxxx>
> > Reported-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/msm/dp/dp_display.c | 40 +++++++++++++++++++++++++++----------
> >   1 file changed, 30 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> > index 01453db..943e4f1 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_display.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> > @@ -113,6 +113,7 @@ struct dp_display_private {
> >          u32 hpd_state;
> >          u32 event_pndx;
> >          u32 event_gndx;
> > +       struct task_struct *ev_tsk;
> >          struct dp_event event_list[DP_EVENT_Q_MAX];
> >          spinlock_t event_lock;
> >
> > @@ -230,6 +231,31 @@ void dp_display_signal_audio_complete(struct msm_dp *dp_display)
> >          complete_all(&dp->audio_comp);
> >   }
> >
> > +static int hpd_event_thread(void *data);
> Is there a reason why this is needed vs. defining the kthread start
> function after hpd_event_thread()?
too many code need to be relocated.
> > +
> > +static void dp_hpd_event_setup(struct dp_display_private *dp_priv)
> Maybe dp_hpd_event_thread_start()?
>
> > +{
> > +       init_waitqueue_head(&dp_priv->event_q);
> > +       spin_lock_init(&dp_priv->event_lock);
> > +
> > +       dp_priv->ev_tsk = kthread_run(hpd_event_thread, dp_priv, "dp_hpd_handler");
> > +
> > +       if (IS_ERR(dp_priv->ev_tsk))
> > +               DRM_ERROR("failed to create DP event thread\n");
> Can we return an error from this function?
>
> > +}
> > +
> > +static void dp_hpd_event_stop(struct dp_display_private *dp_priv)
> Maybe dp_hpd_event_thread_stop()?
>
> > +{
> > +       if (IS_ERR(dp_priv->ev_tsk))
> > +               return;
> If we handled the error then this check becomes impossible.
>
> > +
> > +       kthread_stop(dp_priv->ev_tsk);
> > +
> > +       /* reset event q to empty */
> > +       dp_priv->event_gndx = 0;
> > +       dp_priv->event_pndx = 0;
> > +}
> > +
> >   static int dp_display_bind(struct device *dev, struct device *master,
> >                             void *data)
> >   {
> > @@ -269,6 +295,7 @@ static int dp_display_bind(struct device *dev, struct device *master,
> >          if (rc)
> >                  DRM_ERROR("Audio registration Dp failed\n");
> >
> > +       dp_hpd_event_setup(dp); /* start event thread */
> The comment is useless, please remove.
>
> >   end:
> >          return rc;
> >   }
> > @@ -280,6 +307,8 @@ static void dp_display_unbind(struct device *dev, struct device *master,
> >          struct drm_device *drm = dev_get_drvdata(master);
> >          struct msm_drm_private *priv = drm->dev_private;
> >
> > +       disable_irq(dp->irq);
> Is the disable_irq() necessary? It would be nicer to silence the
> hardware and remove the disable_irq() so that we can reason about the
> code assuming the irq is always enabled after it is requested.
>
> > +       dp_hpd_event_stop(dp); /* stop event thread */
> >          dp_power_client_deinit(dp->power);
> >          dp_aux_unregister(dp->aux);
> >          priv->dp[dp->id] = NULL;