linux-kernel - Re: [PATCH] drm/msm/dp: Sleep properly in dp_hpd

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Date:   Thu, 17 Sep 2020 16:20:48 -0700
From:   khsieh@...eaurora.org
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        Tanmay Shah <tanmay@...eaurora.org>,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH] drm/msm/dp: Sleep properly in dp_hpd_handler kthread

On 2020-09-17 15:44, Stephen Boyd wrote:
> We shouldn't be waiting for an event here with a timeout of 100ms when
> we're not in the 'timeout' arm of the if condition. Instead we should 
> be
> sleeping in the interruptible state (S) until something happens and we
> need to wakeup. Right now this kthread is running almost all the time
> because it sleeps for 100ms, wakes up, sees there's nothing to do, and
> then starts the process all over again. Looking at top it shows up in
> the D state (uninterruptible) because it uses wait_event_timeout(). FIx
> this up.
> 
> Cc: Tanmay Shah <tanmay@...eaurora.org>
> Cc: Kuogee Hsieh <khsieh@...eaurora.org>
> Reported-by: Douglas Anderson <dianders@...omium.org>
> Fixes: 8ede2ecc3e5e ("drm/msm/dp: Add DP compliance tests on
> Snapdragon Chipsets")
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
Reviewed-by: Kuogee Hsieh <khsieh@...eaurora.org>
> ---
> 
> Based on msm-next-dp of https://gitlab.freedesktop.org/drm/msm.git
> 
>  drivers/gpu/drm/msm/dp/dp_display.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c
> b/drivers/gpu/drm/msm/dp/dp_display.c
> index 05a97e097edf..e175aa3fd3a9 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -970,9 +970,8 @@ static int hpd_event_thread(void *data)
>  				(dp_priv->event_pndx == dp_priv->event_gndx),
>  						EVENT_TIMEOUT);
>  		} else {
> -			wait_event_timeout(dp_priv->event_q,
> -				(dp_priv->event_pndx != dp_priv->event_gndx),
> -						EVENT_TIMEOUT);
> +			wait_event_interruptible(dp_priv->event_q,
> +				(dp_priv->event_pndx != dp_priv->event_gndx));
>  		}
>  		spin_lock_irqsave(&dp_priv->event_lock, flag);
>  		todo = &dp_priv->event_list[dp_priv->event_gndx];
> 
> base-commit: 937f941ca06f2f3ab64baebf31be2c16d57ae7b8