linux-kernel - Re: [PATCH] media: ov7670: check status of ov7670

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Message-ID: <20201006124148.GC5682@valkosipuli.retiisi.org.uk>
Date:   Tue, 6 Oct 2020 15:41:48 +0300
From:   Sakari Ailus <sakari.ailus@....fi>
To:     trix@...hat.com
Cc:     corbet@....net, mchehab@...nel.org, natechancellor@...il.com,
        ndesaulniers@...gle.com, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: ov7670: check status of ov7670_read

Hi Tom,

On Fri, Aug 28, 2020 at 07:55:18AM -0700, trix@...hat.com wrote:
> From: Tom Rix <trix@...hat.com>
> 
> clang static analysis flags this representative problem
> 
> drivers/media/i2c/ov7670.c:1463:9: warning: Assigned
>   value is garbage or undefined
>         *value = gain;
>                ^ ~~~~
> 
> gain is set by a successful call to ov7670_read()
> 
> So check that ov7670_read() is successful.
> 
> The remaining static analysis problems are false positives.
> There appears to be a limitation with checking the
> aggregated returns.
> 
> Signed-off-by: Tom Rix <trix@...hat.com>
> ---
>  drivers/media/i2c/ov7670.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/i2c/ov7670.c b/drivers/media/i2c/ov7670.c
> index b42b289faaef..001d4b09db72 100644
> --- a/drivers/media/i2c/ov7670.c
> +++ b/drivers/media/i2c/ov7670.c
> @@ -929,6 +929,8 @@ static int ov7670_set_hw(struct v4l2_subdev *sd, int hstart, int hstop,
>  	ret =  ov7670_write(sd, REG_HSTART, (hstart >> 3) & 0xff);
>  	ret += ov7670_write(sd, REG_HSTOP, (hstop >> 3) & 0xff);
>  	ret += ov7670_read(sd, REG_HREF, &v);
> +	if (ret)
> +		return ret;

Thanks for the patch.

While the patch fixes a bug, could you also fix adding the return values?
These are valid error codes to begin with, but it makes no sense to add
them together.

>  	v = (v & 0xc0) | ((hstop & 0x7) << 3) | (hstart & 0x7);
>  	msleep(10);
>  	ret += ov7670_write(sd, REG_HREF, v);
> @@ -938,6 +940,8 @@ static int ov7670_set_hw(struct v4l2_subdev *sd, int hstart, int hstop,
>  	ret += ov7670_write(sd, REG_VSTART, (vstart >> 2) & 0xff);
>  	ret += ov7670_write(sd, REG_VSTOP, (vstop >> 2) & 0xff);
>  	ret += ov7670_read(sd, REG_VREF, &v);
> +	if (ret)
> +		return ret;
>  	v = (v & 0xf0) | ((vstop & 0x3) << 2) | (vstart & 0x3);
>  	msleep(10);
>  	ret += ov7670_write(sd, REG_VREF, v);
> @@ -1460,6 +1464,8 @@ static int ov7670_g_gain(struct v4l2_subdev *sd, __s32 *value)
>  	unsigned char gain;
>  
>  	ret = ov7670_read(sd, REG_GAIN, &gain);
> +	if (ret)
> +		return ret;
>  	*value = gain;
>  	return ret;
>  }
> @@ -1470,11 +1476,14 @@ static int ov7670_s_gain(struct v4l2_subdev *sd, int value)
>  	unsigned char com8;
>  
>  	ret = ov7670_write(sd, REG_GAIN, value & 0xff);
> +	if (ret)
> +		return ret;
>  	/* Have to turn off AGC as well */
> -	if (ret == 0) {
> -		ret = ov7670_read(sd, REG_COM8, &com8);
> -		ret = ov7670_write(sd, REG_COM8, com8 & ~COM8_AGC);
> -	}
> +	ret = ov7670_read(sd, REG_COM8, &com8);
> +	if (ret)
> +		return ret;
> +	ret = ov7670_write(sd, REG_COM8, com8 & ~COM8_AGC);
> +
>  	return ret;
>  }
>  

-- 
Regards,

Sakari Ailus