asm-generic: delay.h fix udelay and ndelay for 8 bit args (a87e553f) · Commits · 戴 / test

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>

include/asm-generic/delay.h

+27 −6

Original line number	Original line	Diff line number	Diff line
	@@ -10,14 +10,35 @@ extern void __ndelay(unsigned long nsecs);
	extern void __const_udelay(unsigned long xloops);		extern void __const_udelay(unsigned long xloops);
	extern void __delay(unsigned long loops);		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) /		/* 0x10c7 is 2*32 / 1000000 (rounded up) /
	#define udelay(n) (__builtin_constant_p(n) ? \		#define udelay(n) \
	((n) > 20000 ? __bad_udelay() : __const_udelay((n) * 0x10c7ul)) : \		({ \
	__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) /		/* 0x5 is 2*32 / 1000000000 (rounded up) /
	#define ndelay(n) (__builtin_constant_p(n) ? \		#define ndelay(n) \
	((n) > 20000 ? __bad_ndelay() : __const_udelay((n) * 5ul)) : \		({ \
	__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 */		#endif /* __ASM_GENERIC_DELAY_H */

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