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

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Date:   Mon, 11 Apr 2022 20:21:03 -0400
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, agross@...nel.org,
        airlied@...ux.ie, bjorn.andersson@...aro.org, daniel@...ll.ch,
        dmitry.baryshkov@...aro.org, robdclark@...il.com, sean@...rly.run,
        vkoul@...nel.org
Cc:     quic_abhinavk@...cinc.com, quic_aravindh@...cinc.com,
        quic_sbillaka@...cinc.com, freedreno@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dp: stop event kernel thread when DP unbind

Quoting Kuogee Hsieh (2022-04-11 17:08:49)
> 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().
>
> Fixes: e91e3065a806 ("drm/msm/dp: Add DP compliance tests on Snapdragon Chipsets")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>

Should add a Reported-by tag from Dmitry here.

> ---
>  drivers/gpu/drm/msm/dp/dp_display.c | 24 ++++++++++++++++++++++--
>  1 file changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index 01453db..fa1ef8e 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -273,6 +274,8 @@ static int dp_display_bind(struct device *dev, struct device *master,
>         return rc;
>  }
>
> +static void dp_hpd_event_stop(struct dp_display_private *dp_priv);

Why can't the function be defined here?

> +
>  static void dp_display_unbind(struct device *dev, struct device *master,
>                               void *data)
>  {
> @@ -280,6 +283,8 @@ 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);
> +       dp_hpd_event_stop(dp);
>         dp_power_client_deinit(dp->power);
>         dp_aux_unregister(dp->aux);
>         priv->dp[dp->id] = NULL;
> @@ -1054,7 +1059,7 @@ static int hpd_event_thread(void *data)
>
>         dp_priv = (struct dp_display_private *)data;
>
> -       while (1) {
> +       while (!kthread_should_stop()) {
>                 if (timeout_mode) {
>                         wait_event_timeout(dp_priv->event_q,
>                                 (dp_priv->event_pndx == dp_priv->event_gndx),
> @@ -1137,7 +1142,22 @@ static void dp_hpd_event_setup(struct dp_display_private *dp_priv)
>         init_waitqueue_head(&dp_priv->event_q);
>         spin_lock_init(&dp_priv->event_lock);
>
> -       kthread_run(hpd_event_thread, dp_priv, "dp_hpd_handler");
> +       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");

Why can't we error out? Why can't this kthread be started in probe?

> +}
> +
> +static void dp_hpd_event_stop(struct dp_display_private *dp_priv)
> +{
> +       if (IS_ERR(dp_priv->ev_tsk))
> +               return;
> +
> +       kthread_stop(dp_priv->ev_tsk);
> +
> +       /* reset event q to empty */
> +       dp_priv->event_gndx = 0;
> +       dp_priv->event_pndx = 0;
>  }
>