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

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Message-ID: <7529d921-0b12-d162-416d-3542933a0aed@linaro.org>
Date:   Tue, 12 Apr 2022 03:22:59 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>, agross@...nel.org,
        airlied@...ux.ie, bjorn.andersson@...aro.org, daniel@...ll.ch,
        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

On 12/04/2022 03:21, Stephen Boyd wrote:
> 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?

Just my 2c. I don't think starting it in probe is a good idea. The 
driver uses components, so, in my opinion, the thread should be started 
from bind and stopped in unbind.

> 
>> +}
>> +
>> +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;
>>   }
>>


-- 
With best wishes
Dmitry