From: Arnd Bergmann <arnd@arndb.de>
To: Ian Abbott <abbotti@mev.co.uk>,
        H Hartley Sweeten <hsweeten@visionengravers.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>, Amitoj Kaur Chawla <amitoj1606@gmail.com>,
        Bhaktipriya Shridhar <bhaktipriya96@gmail.com>,
        devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org
Subject: [PATCH] staging/comedi/dt282x: avoid integer overflow warning
Date: Mon, 14 Mar 2016 23:48:16 +0100
Message-Id: <1457995713-1517950-1-git-send-email-arnd@arndb.de>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 4832
Lines: 120

gcc-6 warns about passing negative signed integer into swab16()
in the dt282x driver:

drivers/staging/comedi/drivers/dt282x.c: In function 'dt282x_load_changain':
include/uapi/linux/swab.h:14:33: warning: integer overflow in expression [-Woverflow]
  (((__u16)(x) & (__u16)0xff00U) >> 8)))
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
include/uapi/linux/swab.h:107:2: note: in expansion of macro '___constant_swab16'
  ___constant_swab16(x) :   \
  ^~~~~~~~~~~~~~~~~~
include/uapi/linux/byteorder/big_endian.h:34:43: note: in expansion of macro '__swab16'
 #define __cpu_to_le16(x) ((__force __le16)__swab16((x)))
                                           ^~~~~~~~
include/linux/byteorder/generic.h:89:21: note: in expansion of macro '__cpu_to_le16'
 #define cpu_to_le16 __cpu_to_le16
                     ^~~~~~~~~~~~~
arch/arm/include/asm/io.h:250:6: note: in expansion of macro 'cpu_to_le16'
      cpu_to_le16(v),__io(p)); })
      ^~~~~~~~~~~
drivers/staging/comedi/drivers/dt282x.c:566:2: note: in expansion of macro 'outw'
  outw(DT2821_CHANCSR_LLE | DT2821_CHANCSR_NUMB(n),
  ^~~~

The warning makes sense, though the code is correct as far as I
can tell.

This disambiguates the operation by making the constant expressions
we pass here explicitly 'unsigned', which helps to avoid the warning.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/staging/comedi/drivers/dt282x.c | 62 ++++++++++++++++-----------------
 1 file changed, 31 insertions(+), 31 deletions(-)

diff --git a/drivers/staging/comedi/drivers/dt282x.c b/drivers/staging/comedi/drivers/dt282x.c
index 40bf00984fa5..d4d45c759c62 100644
--- a/drivers/staging/comedi/drivers/dt282x.c
+++ b/drivers/staging/comedi/drivers/dt282x.c
@@ -69,48 +69,48 @@
  * Register map
  */
 #define DT2821_ADCSR_REG		0x00
-#define DT2821_ADCSR_ADERR		(1 << 15)
-#define DT2821_ADCSR_ADCLK		(1 << 9)
-#define DT2821_ADCSR_MUXBUSY		(1 << 8)
-#define DT2821_ADCSR_ADDONE		(1 << 7)
-#define DT2821_ADCSR_IADDONE		(1 << 6)
+#define DT2821_ADCSR_ADERR		(1u << 15)
+#define DT2821_ADCSR_ADCLK		(1u << 9)
+#define DT2821_ADCSR_MUXBUSY		(1u << 8)
+#define DT2821_ADCSR_ADDONE		(1u << 7)
+#define DT2821_ADCSR_IADDONE		(1u << 6)
 #define DT2821_ADCSR_GS(x)		(((x) & 0x3) << 4)
 #define DT2821_ADCSR_CHAN(x)		(((x) & 0xf) << 0)
 #define DT2821_CHANCSR_REG		0x02
-#define DT2821_CHANCSR_LLE		(1 << 15)
+#define DT2821_CHANCSR_LLE		(1u << 15)
 #define DT2821_CHANCSR_PRESLA(x)	(((x) & 0xf) >> 8)
 #define DT2821_CHANCSR_NUMB(x)		((((x) - 1) & 0xf) << 0)
 #define DT2821_ADDAT_REG		0x04
 #define DT2821_DACSR_REG		0x06
-#define DT2821_DACSR_DAERR		(1 << 15)
+#define DT2821_DACSR_DAERR		(1u << 15)
 #define DT2821_DACSR_YSEL(x)		((x) << 9)
-#define DT2821_DACSR_SSEL		(1 << 8)
-#define DT2821_DACSR_DACRDY		(1 << 7)
-#define DT2821_DACSR_IDARDY		(1 << 6)
-#define DT2821_DACSR_DACLK		(1 << 5)
-#define DT2821_DACSR_HBOE		(1 << 1)
-#define DT2821_DACSR_LBOE		(1 << 0)
+#define DT2821_DACSR_SSEL		(1u << 8)
+#define DT2821_DACSR_DACRDY		(1u << 7)
+#define DT2821_DACSR_IDARDY		(1u << 6)
+#define DT2821_DACSR_DACLK		(1u << 5)
+#define DT2821_DACSR_HBOE		(1u << 1)
+#define DT2821_DACSR_LBOE		(1u << 0)
 #define DT2821_DADAT_REG		0x08
 #define DT2821_DIODAT_REG		0x0a
 #define DT2821_SUPCSR_REG		0x0c
-#define DT2821_SUPCSR_DMAD		(1 << 15)
-#define DT2821_SUPCSR_ERRINTEN		(1 << 14)
-#define DT2821_SUPCSR_CLRDMADNE		(1 << 13)
-#define DT2821_SUPCSR_DDMA		(1 << 12)
-#define DT2821_SUPCSR_DS_PIO		(0 << 10)
-#define DT2821_SUPCSR_DS_AD_CLK		(1 << 10)
-#define DT2821_SUPCSR_DS_DA_CLK		(2 << 10)
-#define DT2821_SUPCSR_DS_AD_TRIG	(3 << 10)
-#define DT2821_SUPCSR_BUFFB		(1 << 9)
-#define DT2821_SUPCSR_SCDN		(1 << 8)
-#define DT2821_SUPCSR_DACON		(1 << 7)
-#define DT2821_SUPCSR_ADCINIT		(1 << 6)
-#define DT2821_SUPCSR_DACINIT		(1 << 5)
-#define DT2821_SUPCSR_PRLD		(1 << 4)
-#define DT2821_SUPCSR_STRIG		(1 << 3)
-#define DT2821_SUPCSR_XTRIG		(1 << 2)
-#define DT2821_SUPCSR_XCLK		(1 << 1)
-#define DT2821_SUPCSR_BDINIT		(1 << 0)
+#define DT2821_SUPCSR_DMAD		(1u << 15)
+#define DT2821_SUPCSR_ERRINTEN		(1u << 14)
+#define DT2821_SUPCSR_CLRDMADNE		(1u << 13)
+#define DT2821_SUPCSR_DDMA		(1u << 12)
+#define DT2821_SUPCSR_DS_PIO		(0u << 10)
+#define DT2821_SUPCSR_DS_AD_CLK		(1u << 10)
+#define DT2821_SUPCSR_DS_DA_CLK		(2u << 10)
+#define DT2821_SUPCSR_DS_AD_TRIG	(3u << 10)
+#define DT2821_SUPCSR_BUFFB		(1u << 9)
+#define DT2821_SUPCSR_SCDN		(1u << 8)
+#define DT2821_SUPCSR_DACON		(1u << 7)
+#define DT2821_SUPCSR_ADCINIT		(1u << 6)
+#define DT2821_SUPCSR_DACINIT		(1u << 5)
+#define DT2821_SUPCSR_PRLD		(1u << 4)
+#define DT2821_SUPCSR_STRIG		(1u << 3)
+#define DT2821_SUPCSR_XTRIG		(1u << 2)
+#define DT2821_SUPCSR_XCLK		(1u << 1)
+#define DT2821_SUPCSR_BDINIT		(1u << 0)
 #define DT2821_TMRCTR_REG		0x0e
 
 static const struct comedi_lrange range_dt282x_ai_lo_bipolar = {
-- 
2.7.0