linux-kernel - Re: [PATCH 25/25] media: i2c: ccs-core: fix pm_runtime_get

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Message-ID: <20210505103409.GN3@paasikivi.fi.intel.com>
Date:   Wed, 5 May 2021 13:34:09 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc:     linuxarm@...wei.com, mauro.chehab@...wei.com,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: [PATCH 25/25] media: i2c: ccs-core: fix pm_runtime_get_sync()
 usage count

Hi Mauro,

Thanks for the patch.

On Wed, May 05, 2021 at 11:42:15AM +0200, Mauro Carvalho Chehab wrote:
> The pm_runtime_get_sync() internally increments the
> dev->power.usage_count without decrementing it, even on errors.
> 
> There is a bug at ccs_pm_get_init(): when this function returns
> an error, the stream is not started, and RPM usage_count
> should not be incremented. However, if the calls to
> v4l2_ctrl_handler_setup() return errors, it will be kept
> incremented.
> 
> At ccs_suspend() the best is to replace it by the new
> pm_runtime_resume_and_get(), introduced by:
> commit dd8088d5a896 ("PM: runtime: Add pm_runtime_resume_and_get to deal with usage counter")
> in order to properly decrement the usage counter automatically,
> in the case of errors.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>

Could you add Fixes: line and Cc: stable?

The patch that breaks this is 96e3a6b92f23a .

It would be better to fix the bug first so the patch to the stable trees
doesn't need special handling.

> ---
>  drivers/media/i2c/ccs/ccs-core.c | 39 ++++++++++++++++++++------------
>  1 file changed, 24 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/media/i2c/ccs/ccs-core.c b/drivers/media/i2c/ccs/ccs-core.c
> index b05f409014b2..04c3ab9e37b4 100644
> --- a/drivers/media/i2c/ccs/ccs-core.c
> +++ b/drivers/media/i2c/ccs/ccs-core.c
> @@ -1880,21 +1880,33 @@ static int ccs_pm_get_init(struct ccs_sensor *sensor)
>  	struct i2c_client *client = v4l2_get_subdevdata(&sensor->src->sd);
>  	int rval;
>  
> +	/*
> +	 * It can't use pm_runtime_resume_and_get() here, as the driver
> +	 * relies at the returned value to detect if the device was already
> +	 * active or not.
> +	 */
>  	rval = pm_runtime_get_sync(&client->dev);
> -	if (rval < 0) {
> -		pm_runtime_put_noidle(&client->dev);
> +	if (rval < 0)
> +		goto error;
>  
> -		return rval;
> -	} else if (!rval) {
> -		rval = v4l2_ctrl_handler_setup(&sensor->pixel_array->
> -					       ctrl_handler);
> -		if (rval)
> -			return rval;
> +	/* Device was already active, so don't set controls */
> +	if (rval == 1)
> +		return 0;
>  
> -		return v4l2_ctrl_handler_setup(&sensor->src->ctrl_handler);
> -	}
> +	/* Restore V4L2 controls to the suspended device */
> +	rval = v4l2_ctrl_handler_setup(&sensor->pixel_array->ctrl_handler);
> +	if (rval)
> +		goto error;
>  
> +	rval = v4l2_ctrl_handler_setup(&sensor->src->ctrl_handler);
> +	if (rval)
> +		goto error;
> +
> +	/* Keep PM runtime usage_count incremented on success */
>  	return 0;
> +error:
> +	pm_runtime_put_noidle(&client->dev);

This needs to be pm_runtime_put() as the device has been successfully.

> +	return rval;
>  }
>  
>  static int ccs_set_stream(struct v4l2_subdev *subdev, int enable)
> @@ -3089,12 +3101,9 @@ static int __maybe_unused ccs_suspend(struct device *dev)
>  	bool streaming = sensor->streaming;
>  	int rval;
>  
> -	rval = pm_runtime_get_sync(dev);
> -	if (rval < 0) {
> -		pm_runtime_put_noidle(dev);
> -
> +	rval = pm_runtime_resume_and_get(dev);
> +	if (rval < 0)
>  		return rval;
> -	}
>  
>  	if (sensor->streaming)
>  		ccs_stop_streaming(sensor);

-- 
Kind regards,

Sakari Ailus