linux-kernel - Re: [PATCH v1 1/2] media: hi846: fix usage of pm_runtime_get_if_in

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Date:   Wed, 5 Apr 2023 15:52:52 +0300
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Martin Kepplinger <martin.kepplinger@...i.sm>
Cc:     mchehab@...nel.org, laurent.pinchart@...asonboard.com,
        kernel@...i.sm, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] media: hi846: fix usage of
 pm_runtime_get_if_in_use()

Hi Martin,

On Wed, Apr 05, 2023 at 11:29:03AM +0200, Martin Kepplinger wrote:
> pm_runtime_get_if_in_use() does not only return nonzero values when
> the device is in use, it can return a negative errno too.
> 
> And especially during resuming from system suspend, when runtime pm
> is not yet up again, this can very well happen. And in such a case
> the subsequent pm_runtime_put() call would result in a refcount underflow!

I think this issue should have a more generic solution, it's very difficult
to address this in drivers only with the current APIs.

pm_runtime_get_if_in_use() will also return an error if runtime PM is
disabled, so this patch will break the driver for that configuration.

> 
> Fix it by correctly using pm_runtime_get_if_in_use().
> 
> Signed-off-by: Martin Kepplinger <martin.kepplinger@...i.sm>
> ---
>  drivers/media/i2c/hi846.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/i2c/hi846.c b/drivers/media/i2c/hi846.c
> index 5b5ea5425e984..0b0eda2e223cd 100644
> --- a/drivers/media/i2c/hi846.c
> +++ b/drivers/media/i2c/hi846.c
> @@ -1544,7 +1544,7 @@ static int hi846_set_ctrl(struct v4l2_ctrl *ctrl)
>  					 exposure_max);
>  	}
>  
> -	if (!pm_runtime_get_if_in_use(&client->dev))
> +	if (pm_runtime_get_if_in_use(&client->dev) <= 0)
>  		return 0;
>  
>  	switch (ctrl->id) {

-- 
Kind regards,

Sakari Ailus