From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
With a non-constant 8-bit argument, a call to udelay() generates a warning:
drivers/gpu/drm/radeon/atom.c: In function 'atom_op_delay':
drivers/gpu/drm/radeon/atom.c:654: warning: comparison is always false due to limited range of data type
The code looks like it works OK with an 8-bit arg, and the calling code is
doing nothing wrong, so udelay() needs fixing.
Fixing it was rather tricky. Simply typecasting `n' in the comparison with
20000 didn't change anything. Hence the divide-by-20000 trick.
Using a do{}while loop didn't work because udelay() is used in ?: statements,
hence the ({...}) construct.
While I was there I replaced the brain-bending ?:?:?: mess with nice if/else
code.
Probably other architectures are generating the same warning and can use a
similar change.
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: <linux-arch@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/delay.h | 33 +++++++++++++++++++++++++++------
1 file changed, 27 insertions(+), 6 deletions(-)
diff -puN arch/x86/include/asm/delay.h~arch-x86-include-asm-delayh-fix-udelay-and-ndelay-for-8-bit-args arch/x86/include/asm/delay.h
--- a/arch/x86/include/asm/delay.h~arch-x86-include-asm-delayh-fix-udelay-and-ndelay-for-8-bit-args
+++ a/arch/x86/include/asm/delay.h
@@ -16,15 +16,36 @@ extern void __ndelay(unsigned long nsecs
extern void __const_udelay(unsigned long xloops);
extern void __delay(unsigned long loops);
+/*
+ * The weird n/20000 thing suppresses a "comparison is always false due to
+ * limited range of data type" warning with non-const 8-bit arguments.
+ */
+
/* 0x10c7 is 2**32 / 1000000 (rounded up) */
-#define udelay(n) (__builtin_constant_p(n) ? \
- ((n) > 20000 ? __bad_udelay() : __const_udelay((n) * 0x10c7ul)) : \
- __udelay(n))
+#define udelay(n) \
+ ({ \
+ if (__builtin_constant_p(n)) { \
+ if ((n) / 20000 >= 1) \
+ __bad_udelay(); \
+ else \
+ __const_udelay((n) * 0x10c7ul); \
+ } else { \
+ __udelay(n); \
+ } \
+ })
/* 0x5 is 2**32 / 1000000000 (rounded up) */
-#define ndelay(n) (__builtin_constant_p(n) ? \
- ((n) > 20000 ? __bad_ndelay() : __const_udelay((n) * 5ul)) : \
- __ndelay(n))
+#define ndelay(n) \
+ ({ \
+ if (__builtin_constant_p(n)) { \
+ if ((n) / 20000 >= 1) \
+ __bad_ndelay(); \
+ else \
+ __const_udelay((n) * 5ul); \
+ } else { \
+ __ndelay(n); \
+ } \
+ })
void use_tsc_delay(void);
_
--
To unsubscribe from this list: send the line "unsubscribe linux-arch" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
