linux-kernel - Re: [PATCH] drm/omap: Fix runtime PM imbalance in dsi_runtime

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Message-ID: <5123d7ae-f491-d2d2-788d-b5250ae9e31d@ti.com>
Date:   Fri, 21 Aug 2020 15:06:59 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Dinghao Liu <dinghao.liu@....edu.cn>, <kjlu@....edu>
CC:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Sebastian Reichel <sebastian.reichel@...labora.com>,
        Tony Lindgren <tony@...mide.com>,
        zhengbin <zhengbin13@...wei.com>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/omap: Fix runtime PM imbalance in dsi_runtime_get

Hi,

On 21/08/2020 10:45, Dinghao Liu wrote:
> pm_runtime_get_sync() increments the runtime PM usage counter
> even when it returns an error code. However, users of
> dsi_runtime_get(), a direct wrapper of pm_runtime_get_sync(),
> assume that PM usage counter will not change on error. Thus a
> pairing decrement is needed on the error handling path to keep
> the counter balanced.
> 
> Fixes: 4fbafaf371be7 ("OMAP: DSS2: Use PM runtime & HWMOD support")
> Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> ---
>  drivers/gpu/drm/omapdrm/dss/dsi.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.c b/drivers/gpu/drm/omapdrm/dss/dsi.c
> index eeccf40bae41..973bfa14a104 100644
> --- a/drivers/gpu/drm/omapdrm/dss/dsi.c
> +++ b/drivers/gpu/drm/omapdrm/dss/dsi.c
> @@ -1112,8 +1112,11 @@ static int dsi_runtime_get(struct dsi_data *dsi)
>  	DSSDBG("dsi_runtime_get\n");
>  
>  	r = pm_runtime_get_sync(dsi->dev);
> -	WARN_ON(r < 0);
> -	return r < 0 ? r : 0;
> +	if (WARN_ON(r < 0)) {
> +		pm_runtime_put_noidle(dsi->dev);
> +		return r;
> +	}
> +	return 0;
>  }

Thanks! Good catch. I think this is broken in all the other modules in omapdrm too (e.g. dispc.c,
venc.c, etc).

Would you like to update the patch to cover the whole omapdrm?

 Tomi

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