linux-kernel - Re: [PATCH v3 02/14] media: mt9m111: prevent module removal while in use

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Message-ID: <4a60c89e-f183-5c92-8c5d-e5d75767c10b@xs4all.nl>
Date:	Sat, 13 Aug 2016 20:40:17 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	Robert Jarzmik <robert.jarzmik@...e.fr>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Jiri Kosina <trivial@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org
Subject: Re: [PATCH v3 02/14] media: mt9m111: prevent module removal while in
 use

On 08/08/2016 09:30 PM, Robert Jarzmik wrote:
> The mt9m111 can be a removable module : the only case where the module
> should be kept loaded is while it is used, ie. while an active
> transation is ongoing on it.
> 
> The notion of active transaction is mapped on the power state of the
> module : if powered on the removal is prohibited.

I don't really see the purpose of this patch: if this driver is loaded
by a platform driver (such as pxa_camera), then the module count should be
1 and it isn't possible to unload.

So you shouldn't need this patch. Am I missing something?

No other driver in drivers/media/i2c does something like this.

Regards,

	Hans

> 
> Signed-off-by: Robert Jarzmik <robert.jarzmik@...e.fr>
> ---
>  drivers/media/i2c/soc_camera/mt9m111.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/i2c/soc_camera/mt9m111.c b/drivers/media/i2c/soc_camera/mt9m111.c
> index a7efaa5964d1..ea5b5e709402 100644
> --- a/drivers/media/i2c/soc_camera/mt9m111.c
> +++ b/drivers/media/i2c/soc_camera/mt9m111.c
> @@ -780,23 +780,33 @@ static int mt9m111_power_on(struct mt9m111 *mt9m111)
>  	struct i2c_client *client = v4l2_get_subdevdata(&mt9m111->subdev);
>  	int ret;
>  
> +	if (!try_module_get(THIS_MODULE))
> +		return -ENXIO;
> +
>  	ret = v4l2_clk_enable(mt9m111->clk);
>  	if (ret < 0)
> -		return ret;
> +		goto out_module_put;
>  
>  	ret = mt9m111_resume(mt9m111);
>  	if (ret < 0) {
>  		dev_err(&client->dev, "Failed to resume the sensor: %d\n", ret);
> -		v4l2_clk_disable(mt9m111->clk);
> +		goto out_clk_disable;
>  	}
>  
>  	return ret;
> +
> +out_clk_disable:
> +	v4l2_clk_disable(mt9m111->clk);
> +out_module_put:
> +	module_put(THIS_MODULE);
> +	return ret;
>  }
>  
>  static void mt9m111_power_off(struct mt9m111 *mt9m111)
>  {
>  	mt9m111_suspend(mt9m111);
>  	v4l2_clk_disable(mt9m111->clk);
> +	module_put(THIS_MODULE);
>  }
>  
>  static int mt9m111_s_power(struct v4l2_subdev *sd, int on)
>