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Date:   Tue, 19 Apr 2022 14:44:07 +0200
From:   Maxime Ripard <maxime@cerno.tech>
To:     Miaoqian Lin <linmq006@gmail.com>
Cc:     Emma Anholt <emma@anholt.net>, David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>, Eric Anholt <eric@anholt.net>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/vc4: Fix pm_runtime_get_sync() error checking
Message-ID: <20220419124407.ugzl7hknsytbhrmr@houat>
References: <20220412070458.21819-1-linmq006@gmail.com>
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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.
>=20
> Fixes: 4078f5757144 ("drm/vc4: Add DSI driver")
> Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
> ---
>  drivers/gpu/drm/vc4/vc4_dsi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> 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;
> =20
>  	ret =3D 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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