linux-kernel - Re: [PATCH v2] drm/vc4: Fix pm_runtime_get

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Date:   Wed, 20 Apr 2022 09:51:08 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Miaoqian Lin <linmq006@...il.com>
Cc:     Emma Anholt <emma@...olt.net>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, Eric Anholt <eric@...olt.net>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/vc4: Fix pm_runtime_get_sync() usage

On Wed, Apr 20, 2022 at 12:49:48AM +0000, Miaoqian Lin wrote:
> If the device is already in a runtime PM enabled state
> pm_runtime_get_sync() will return 1, so a test for negative
> value should be used to check for errors.
> 
> Also, we need to call pm_runtime_put_noidle() when pm_runtime_get_sync()
> fails, so use pm_runtime_resume_and_get() instead. this function
> will handle this.
> 
> Fixes: 4078f5757144 ("drm/vc4: Add DSI driver")
> Signed-off-by: Miaoqian Lin <linmq006@...il.com>
> ---
> change in v2:
> - switch to pm_runtime_resume_and_get() to fix refcount leak.
> ---
>  drivers/gpu/drm/vc4/vc4_dsi.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> index 752f921735c6..9d7ffaf6bc70 100644
> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> @@ -846,8 +846,8 @@ static void vc4_dsi_encoder_enable(struct drm_encoder *encoder)
>  	unsigned long phy_clock;
>  	int ret;
>  
> -	ret = pm_runtime_get_sync(dev);
> -	if (ret) {
> +	ret = pm_runtime_resume_and_get(dev);
> +	if (ret < 0) {

pm_runtime_resume_and_get will return 0 on success, so the previous check was correct

Maxime

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