linux-kernel - Re: [PATCH v3] drm/msm/dp: stop event kernel thread when DP unbind

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Message-ID: <be3141cb-1fa9-4a9c-6b18-c0d73b9efe80@linaro.org>
Date:   Thu, 14 Apr 2022 22:59:54 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, robdclark@...il.com,
        sean@...rly.run, swboyd@...omium.org, vkoul@...nel.org,
        daniel@...ll.ch, airlied@...ux.ie, agross@...nel.org,
        bjorn.andersson@...aro.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 v3] drm/msm/dp: stop event kernel thread when DP unbind

On 14/04/2022 20:25, Kuogee Hsieh wrote:
> 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()
> 
> Changes in v3:
> -- disable all HDP interrupts at unbind
> -- replace dp_hpd_event_setup() with dp_hpd_event_thread_start()
> -- replace dp_hpd_event_stop() with dp_hpd_event_thread_stop()
> -- move init_waitqueue_head(&dp->event_q) to probe()
> -- move spin_lock_init(&dp->event_lock) to probe()
> 
> 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 | 42 ++++++++++++++++++++++++++++---------
>   1 file changed, 32 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..0b9a96f 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 +231,29 @@ void dp_display_signal_audio_complete(struct msm_dp *dp_display)
>   	complete_all(&dp->audio_comp);
>   }
>   
> +static int hpd_event_thread(void *data);
> +
> +static int dp_hpd_event_thread_start(struct dp_display_private *dp_priv)
> +{
> +	int err = 0;
> +
> +	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");
> +		err = PTR_ERR(dp_priv->ev_tsk);
> +	}
> +	return err;

Generally the preference is for the following style:

if (error) {
    return error;
}

return 0;

It makes it clear that at the end the function succeeds.


> +}
> +
> +static void dp_hpd_event_thread_stop(struct dp_display_private *dp_priv)
> +{
> +	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 +293,7 @@ static int dp_display_bind(struct device *dev, struct device *master,
>   	if (rc)
>   		DRM_ERROR("Audio registration Dp failed\n");

Isn't 'goto end' missing here?

That's why it's suggested not to mix error and success paths.

>   
> +	rc = dp_hpd_event_thread_start(dp);
>   end:
>   	return rc;
>   }
> @@ -280,6 +305,9 @@ 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 all HPD interrupts */
> +	dp_catalog_hpd_config_intr(dp->catalog, DP_DP_HPD_INT_MASK, false);

Generic nit: if we had _enable and _disable functions, one wouldn't need 
the comment here. It would be obvious from the code itself.


> +	dp_hpd_event_thread_stop(dp);
>   	dp_power_client_deinit(dp->power);
>   	dp_aux_unregister(dp->aux);
>   	priv->dp[dp->id] = NULL;
> @@ -1054,7 +1082,7 @@ 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),
> @@ -1132,13 +1160,6 @@ static int hpd_event_thread(void *data)
>   	return 0;
>   }
>   
> -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");
> -}
>   
>   static irqreturn_t dp_display_irq_handler(int irq, void *dev_id)
>   {
> @@ -1266,7 +1287,10 @@ static int dp_display_probe(struct platform_device *pdev)
>   		return -EPROBE_DEFER;
>   	}
>   
> +	/* setup event q */
>   	mutex_init(&dp->event_mutex);
> +	init_waitqueue_head(&dp->event_q);
> +	spin_lock_init(&dp->event_lock);
>   
>   	/* Store DP audio handle inside DP display */
>   	dp->dp_display.dp_audio = dp->audio;
> @@ -1441,8 +1465,6 @@ void msm_dp_irq_postinstall(struct msm_dp *dp_display)
>   
>   	dp = container_of(dp_display, struct dp_display_private, dp_display);
>   
> -	dp_hpd_event_setup(dp);
> -
>   	dp_add_event(dp, EV_HPD_INIT_SETUP, 0, 100);
>   }
>   


-- 
With best wishes
Dmitry