linux-kernel - [PATCH v3] media: v4l2-device.h: Explicitly compare grp{id,mask} to zero in v4l2

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Message-Id: <20191208211139.18514-1-natechancellor@gmail.com>
Date:   Sun,  8 Dec 2019 14:11:40 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nathan Chancellor <natechancellor@...il.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH v3] media: v4l2-device.h: Explicitly compare grp{id,mask} to zero in v4l2_device macros

When building with Clang + -Wtautological-constant-compare, several of
the ivtv and cx18 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
 [-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 warning happens 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. The ultimate goal is to enable
-Wtautological-compare globally because there are several subwarnings
that would be helpful to have.

For visual consistency and avoidance of these warnings in the future,
all of the implicitly boolean conversions in the v4l2_device macros
are converted to explicit ones as well.

Link: https://github.com/ClangBuiltLinux/linux/issues/752
Reviewed-by: Ezequiel Garcia <ezequiel@...labora.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---

v1 -> v2: https://lore.kernel.org/lkml/20191024201240.49063-1-natechancellor@gmail.com/

* Fix typo in commit message
* Add Nick's Reviewed-by.

v2 -> v3: https://lore.kernel.org/lkml/20191105045907.26123-1-natechancellor@gmail.com/

* Improve reasoning for change (Ezequiel)
* Patch all implicit boolean conversions (Ezequiel)
* Add Ezequiel's reviewed-by.

 include/media/v4l2-device.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/media/v4l2-device.h b/include/media/v4l2-device.h
index 5f36e0d2ede6..95353ae476a1 100644
--- a/include/media/v4l2-device.h
+++ b/include/media/v4l2-device.h
@@ -371,7 +371,7 @@ static inline bool v4l2_device_supports_requests(struct v4l2_device *v4l2_dev)
 		struct v4l2_subdev *__sd;				\
 									\
 		__v4l2_device_call_subdevs_p(v4l2_dev, __sd,		\
-			!(grpid) || __sd->grp_id == (grpid), o, f ,	\
+			(grpid) == 0 || __sd->grp_id == (grpid), o, f ,	\
 			##args);					\
 	} while (0)
 
@@ -403,7 +403,7 @@ static inline bool v4l2_device_supports_requests(struct v4l2_device *v4l2_dev)
 ({									\
 	struct v4l2_subdev *__sd;					\
 	__v4l2_device_call_subdevs_until_err_p(v4l2_dev, __sd,		\
-			!(grpid) || __sd->grp_id == (grpid), o, f ,	\
+			(grpid) == 0 || __sd->grp_id == (grpid), o, f ,	\
 			##args);					\
 })
 
@@ -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)
 
 /**
@@ -462,8 +462,8 @@ static inline bool v4l2_device_supports_requests(struct v4l2_device *v4l2_dev)
 ({									\
 	struct v4l2_subdev *__sd;					\
 	__v4l2_device_call_subdevs_until_err_p(v4l2_dev, __sd,		\
-			!(grpmsk) || (__sd->grp_id & (grpmsk)), o, f ,	\
-			##args);					\
+			(grpmsk) == 0 || (__sd->grp_id & (grpmsk)), o,	\
+			f , ##args);					\
 })
 
 
-- 
2.24.0