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

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Message-ID: <02faf872-8fef-342a-d070-67b68953b5f8@quicinc.com>
Date:   Thu, 14 Apr 2022 10:15:51 -0700
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     Stephen Boyd <swboyd@...omium.org>, <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 v2] drm/msm/dp: stop event kernel thread when DP unbind


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@...cinc.com>
>> Reported-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>> ---
>>   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;