[RESEND] floppy: fix harmless clang build warning
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Message ID 20190619131959.2055400-1-arnd@arndb.de
State New
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Series
  • [RESEND] floppy: fix harmless clang build warning
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Commit Message

Arnd Bergmann June 19, 2019, 1:19 p.m. UTC
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@hpe.com>
Cc: Keith Busch <kbusch@kernel.org>
Link: https://patchwork.kernel.org/patch/10851841/
Signed-off-by: Arnd Bergmann <arnd@arndb.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(-)

Comments

Jens Axboe June 20, 2019, 7:36 a.m. UTC | #1
On 6/19/19 7:19 AM, Arnd Bergmann wrote:
> 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.

Applied, thanks.

Patch
diff mbox series

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 */