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SubjectRe: [PATCH v2] media: v4l2-device.h: Explicitly compare grpmask to zero in v4l2_device_mask_call_all
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(Adding Hans)

Hi Nathan, Nick,

Thanks for the patch (and the patience).

On Mon, 2019-11-04 at 21:59 -0700, Nathan Chancellor wrote:
> When building with Clang + -Wtautological-constant-compare, several of
> the ivtv drivers warn along the lines of:
>

Nitpick: s/ivtv/ivtv and cx18

> drivers/media/pci/cx18/cx18-driver.c:1005:21: warning: converting the
> result of '<<' to a boolean always evaluates to true
> [-Wtautological-constant-compare]
> cx18_call_hw(cx, CX18_HW_GPIO_RESET_CTRL,
> ^
> drivers/media/pci/cx18/cx18-cards.h:18:37: note: expanded from macro
> 'CX18_HW_GPIO_RESET_CTRL'
> #define CX18_HW_GPIO_RESET_CTRL (1 << 6)
> ^
> 1 warning generated.
>
> This is because the shift operation is implicitly converted to a boolean
> in v4l2_device_mask_call_all before being negated. This can be solved by
> just comparing the mask result to 0 explicitly so that there is no
> boolean conversion.
>

Perhaps it's interesting to mention the reason for this change,
which you mentioned as a comment before:

"""
The ultimate goal is to get
-Wtautological-compare enabled because there are several subwarnings
that would be helpful to have and right now they are all disabled.
"""

> Link: https://github.com/ClangBuiltLinux/linux/issues/752
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>
> v1 -> v2: https://lore.kernel.org/lkml/20191024201240.49063-1-natechancellor@gmail.com/
>
> * Fix typo in commit message
> * Add Nick's Reviewed-by.
>
> include/media/v4l2-device.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/media/v4l2-device.h b/include/media/v4l2-device.h
> index e0b8f2602670..8564b3227887 100644
> --- a/include/media/v4l2-device.h
> +++ b/include/media/v4l2-device.h
> @@ -431,8 +431,8 @@ static inline bool v4l2_device_supports_requests(struct v4l2_device *v4l2_dev)
> struct v4l2_subdev *__sd; \
> \
> __v4l2_device_call_subdevs_p(v4l2_dev, __sd, \
> - !(grpmsk) || (__sd->grp_id & (grpmsk)), o, f , \
> - ##args); \
> + (grpmsk) == 0 || (__sd->grp_id & (grpmsk)), o, \
> + f , ##args); \
> } while (0)
>
> /**

The change is small enough and if it helps enabling helpful
warnings, then it seems a good idea.

Reviewed-by: Ezequiel Garcia <ezequiel@collabora.com>

For consistency, it would be good to also patch the other case(s).

Thanks,
Ezequiel

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