Re: [PATCH v2 19/26] media: ov9650: fix bogus warnings

[Nicholas Mc Guire <der.herr@hofr.at>]

On Wed, Nov 01, 2017 at 05:05:56PM -0400, Mauro Carvalho Chehab wrote:
> The smatch logic gets confused with the syntax used to check if the
> ov9650x_read() reads succedded:
> 	drivers/media/i2c/ov9650.c:895 __g_volatile_ctrl() error: uninitialized symbol 'reg2'.
> 	drivers/media/i2c/ov9650.c:895 __g_volatile_ctrl() error: uninitialized symbol 'reg1'.
> 
> There's nothing wrong with the original logic, except that
> it is a little more harder to review.

Maybe I do not understand the original logic correctly but
ov965x_read(...) is passing on the return value from 
i2c_transfer() -> __i2c_transfer() and thus if one of those
calls would have been a negativ error status it would have simply
executed the next call to ov965x_read() and if that 
call would have suceeded it would eventually reach the
line " exposure = ((reg2 & 0x3f) << 10) | (reg1 << 2) |..."
with the potential to operate on uninitialized registers reg0/1/2
the current code sems only to handle error conditions in the last
call to ov965x_read() correctly.

I think this is actually not an equivalent transform but a bug-fix
of  case V4L2_CID_EXPOSURE_AUTO: (aside from being a code inconsistency)
So should this not carry a 
 Fixes: 84a15ded76ec ("[media] V4L: Add driver for OV9650/52 image sensors")
tag ?

thx!
hofrat

> 
> So, let's stick with the syntax that won't cause read
> issues.
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Reviewed-by: Nicholas Mc Guire <hofrat@osadl.org>

> ---
>  drivers/media/i2c/ov9650.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/i2c/ov9650.c b/drivers/media/i2c/ov9650.c
> index 69433e1e2533..e519f278d5f9 100644
> --- a/drivers/media/i2c/ov9650.c
> +++ b/drivers/media/i2c/ov9650.c
> @@ -886,10 +886,12 @@ static int __g_volatile_ctrl(struct ov965x *ov965x, struct v4l2_ctrl *ctrl)
>  		if (ctrl->val == V4L2_EXPOSURE_MANUAL)
>  			return 0;
>  		ret = ov965x_read(client, REG_COM1, &reg0);
> -		if (!ret)
> -			ret = ov965x_read(client, REG_AECH, &reg1);
> -		if (!ret)
> -			ret = ov965x_read(client, REG_AECHM, &reg2);
> +		if (ret < 0)
> +			return ret;
> +		ret = ov965x_read(client, REG_AECH, &reg1);
> +		if (ret < 0)
> +			return ret;
> +		ret = ov965x_read(client, REG_AECHM, &reg2);
>  		if (ret < 0)
>  			return ret;
>  		exposure = ((reg2 & 0x3f) << 10) | (reg1 << 2) |
> -- 
> 2.13.6
>