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

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Date:   Tue, 19 Apr 2022 14:44:07 +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] drm/vc4: Fix pm_runtime_get_sync() error checking

Hi,

On Tue, Apr 12, 2022 at 07:04:57AM +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.
> 
> Fixes: 4078f5757144 ("drm/vc4: Add DSI driver")
> Signed-off-by: Miaoqian Lin <linmq006@...il.com>
> ---
>  drivers/gpu/drm/vc4/vc4_dsi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> index 752f921735c6..26aa7d1fa421 100644
> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> @@ -847,7 +847,7 @@ static void vc4_dsi_encoder_enable(struct drm_encoder *encoder)
>  	int ret;
>  
>  	ret = pm_runtime_get_sync(dev);
> -	if (ret) {
> +	if (ret < 0) {
>  		DRM_ERROR("Failed to runtime PM enable on DSI%d\n", dsi->variant->port);
>  		return;
>  	}

We also don't put back our reference after an error. I think a better
fix would be to switch to pm_runtime_resume_and_get.

Maxime

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