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

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Date:   Fri, 28 Aug 2020 08:13:02 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     trix@...hat.com
Cc:     Jonathan Corbet <corbet@....net>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        linux-media@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Huckleberry <nhuck15@...il.com>
Subject: Re: [PATCH] media: ov7670: check status of ov7670_read

On Fri, Aug 28, 2020 at 7:55 AM <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()

Indeed, it looks like gain is only valid if the return value from
ov7670_read() is >= 0.  Would it be simpler to just initialize gain to
0 in ov7670_g_gain?

Side question; I'm super happy to see someone sending patches for
things identified by clang's static analyzer.  I'm curious, Tom, how
did you run it?  Did you use the recently landed in kbuild-next
support for the make target `make clang-analyzer`?

>
> 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;
>         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;
>  }
>
> --
> 2.18.1
>


-- 
Thanks,
~Nick Desaulniers