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Subject[PATCH] media: v4l2-device.h: Explicitly compare grpmask to zero in v4l2_device_mask_call_all
When building with Clang + -Wtautological-constant-compare, several of
the ivtv drivers warn along the lines of:

drivers/media/pci/cx18/cx18-driver.c:1005:21: warning: converting the
result of '<<' to a boolean always evaluates to true
cx18_call_hw(cx, CX18_HW_GPIO_RESET_CTRL,
drivers/media/pci/cx18/cx18-cards.h:18:37: note: expanded from macro
#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 explicity so that there is no
boolean conversion.

Signed-off-by: Nathan Chancellor <>

I am aware that there is suddenly a style mismatch (some macros using
!(grpmask) and this one using (grpmask) == 0) but I chose to display the
minimal fix. If you want me to update all the macros to use this style,
I'd be happy to in a followup patch.

There are 19 of these warnings in the drivers/media/pci folder, which
can be seen here:

This is the simplest fix but if you all prefer an alternative one, I
would be happy to see/review/test it. 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:

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)

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