linux-kernel - [PATCH] [RESEND] floppy: fix harmless clang build warning

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Message-Id: <20190619131959.2055400-1-arnd@arndb.de>
Date:   Wed, 19 Jun 2019 15:19:44 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Jiri Kosina <jikos@...nel.org>, Jens Axboe <axboe@...nel.dk>
Cc:     Arnd Bergmann <arnd@...db.de>, Robert Elliott <elliott@....com>,
        Keith Busch <kbusch@...nel.org>,
        Hannes Reinecke <hare@...e.de>, Omar Sandoval <osandov@...com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Andy Whitcroft <apw@...onical.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] [RESEND] floppy: fix harmless clang build warning

clang warns about unusual code in floppy.c that looks like it
was intended to be a bit mask operation, checking for a specific
bit in the UDP->cmos variable (FLOPPY1_TYPE expands to '4' on
ARM):

drivers/block/floppy.c:3902:17: error: use of logical '&&' with constant operand [-Werror,-Wconstant-logical-operand]
        if (!UDP->cmos && FLOPPY1_TYPE)
                       ^  ~~~~~~~~~~~~
drivers/block/floppy.c:3902:17: note: use '&' for a bitwise operation
        if (!UDP->cmos && FLOPPY1_TYPE)

The check here is redundant anyway, if FLOPPY1_TYPE is zero, then
assigning it to a zero UDP->cmos field does not change anything,
so removing the extra check here has no effect other than shutting
up the warning.

On x86, this will no longer read a hardware register, as the
FLOPPY1_TYPE macro is not expanded if UDP->cmos is already
zero, but the result is the same.

Cc: Robert Elliott <elliott@....com>
Cc: Keith Busch <kbusch@...nel.org>
Link: https://patchwork.kernel.org/patch/10851841/
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
The original patch did not get merged since there was some
discussion (see link), but as far as I can tell, the outcome
was that it's harmless so I just summarized the findings
above. The patch is unchanged from March.
---
 drivers/block/floppy.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 9fb9b312ab6b..b933a7eea52b 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -3900,7 +3900,7 @@ static void __init config_types(void)
 	if (!UDP->cmos)
 		UDP->cmos = FLOPPY0_TYPE;
 	drive = 1;
-	if (!UDP->cmos && FLOPPY1_TYPE)
+	if (!UDP->cmos)
 		UDP->cmos = FLOPPY1_TYPE;
 
 	/* FIXME: additional physical CMOS drive detection should go here */
-- 
2.20.0