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asm-generic: delay.h fix udelay and ndelay for 8 bit args 

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.

[Taken from the x86 tree and moved to asm-generic by Jonas Bonn]

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jonas Bonn <jonas@southpole.se>
This commit is contained in:
Andrew Morton 2011-07-18 15:28:20 +02:00 committed by Jonas Bonn
parent 30ab2b034f
commit a87e553fab
1 changed files with 27 additions and 6 deletions
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33
include/asm-generic/delay.h
View File

@ -10,14 +10,35 @@ 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); \
} \
})
#endif /* __ASM_GENERIC_DELAY_H */