linux-kernel - [PATCH] [v2] platform/surface: aggregator: avoid clang -Wconstant-conversion warning

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Message-Id: <20210514200453.1542978-1-arnd@kernel.org>
Date:   Fri, 14 May 2021 22:04:36 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Maximilian Luz <luzmaximilian@...il.com>,
        Hans de Goede <hdegoede@...hat.com>
Cc:     Arnd Bergmann <arnd@...db.de>, platform-driver-x86@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH] [v2] platform/surface: aggregator: avoid clang -Wconstant-conversion warning

From: Arnd Bergmann <arnd@...db.de>

Clang complains about the assignment of SSAM_ANY_IID to
ssam_device_uid->instance:

drivers/platform/surface/surface_aggregator_registry.c:478:25: error: implicit conversion from 'int' to '__u8' (aka 'unsigned char') changes value from 65535 to 255 [-Werror,-Wconstant-conversion]
        { SSAM_VDEV(HUB, 0x02, SSAM_ANY_IID, 0x00) },
        ~                      ^~~~~~~~~~~~
include/linux/surface_aggregator/device.h:71:23: note: expanded from macro 'SSAM_ANY_IID'
 #define SSAM_ANY_IID            0xffff
                                ^~~~~~
include/linux/surface_aggregator/device.h:126:63: note: expanded from macro 'SSAM_VDEV'
        SSAM_DEVICE(SSAM_DOMAIN_VIRTUAL, SSAM_VIRTUAL_TC_##cat, tid, iid, fun)
                                                                     ^~~
include/linux/surface_aggregator/device.h:102:41: note: expanded from macro 'SSAM_DEVICE'
        .instance = ((iid) != SSAM_ANY_IID) ? (iid) : 0,                        \
                                               ^~~

The assignment doesn't actually happen, but clang checks the type limits
before checking whether this assignment is reached. Replace the ?:
operator with a __builtin_choose_expr() invocation that avoids the
warning for the untaken part.

Fixes: eb0e90a82098 ("platform/surface: aggregator: Add dedicated bus and device type")
Cc: platform-driver-x86@...r.kernel.org
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
v2: use __builtin_choose_expr() instead of a cast to shut up the warning
---
 include/linux/surface_aggregator/device.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/surface_aggregator/device.h b/include/linux/surface_aggregator/device.h
index 4441ad667c3f..6ff9c58b3e17 100644
--- a/include/linux/surface_aggregator/device.h
+++ b/include/linux/surface_aggregator/device.h
@@ -98,9 +98,9 @@ struct ssam_device_uid {
 		     | (((fun) != SSAM_ANY_FUN) ? SSAM_MATCH_FUNCTION : 0),	\
 	.domain   = d,								\
 	.category = cat,							\
-	.target   = ((tid) != SSAM_ANY_TID) ? (tid) : 0,			\
-	.instance = ((iid) != SSAM_ANY_IID) ? (iid) : 0,			\
-	.function = ((fun) != SSAM_ANY_FUN) ? (fun) : 0				\
+	.target   = __builtin_choose_expr((tid) != SSAM_ANY_TID, (tid), 0),	\
+	.instance = __builtin_choose_expr((iid) != SSAM_ANY_IID, (iid), 0),	\
+	.function = __builtin_choose_expr((fun) != SSAM_ANY_FUN, (fun), 0)
 
 /**
  * SSAM_VDEV() - Initialize a &struct ssam_device_id as virtual device with
-- 
2.29.2