The patch titled
arch/x86/include/asm/delay.h: fix udelay() and ndelay() for 8-bit args
has been added to the -mm tree. Its filename is
arch-x86-include-asm-delayh-fix-udelay-and-ndelay-for-8-bit-args.patch
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------------------------------------------------------
Subject: arch/x86/include/asm/delay.h: fix udelay() and ndelay() for 8-bit args
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);
_
Patches currently in -mm which might be from akpm@xxxxxxxxxxxxxxxxxxxx are
origin.patch
linux-next.patch
linux-next-rejects.patch
next-remove-localversion.patch
i-need-old-gcc.patch
arch-alpha-kernel-systblss-remove-debug-check.patch
mm-vmap-area-cache.patch
arch-x86-include-asm-delayh-fix-udelay-and-ndelay-for-8-bit-args.patch
drivers-gpu-drm-radeon-atomc-fix-warning.patch
leds-convert-bd2802-driver-to-dev_pm_ops-fix.patch
leds-route-kbd-leds-through-the-generic-leds-layer.patch
backlight-add-backlight-type-fix.patch
backlight-add-backlight-type-fix-fix.patch
fs-ocfs2-dlm-dlmdomainc-avoid-a-gfp_atomic-allocation.patch
drivers-message-fusion-mptsasc-fix-warning.patch
drbd-fix-warning.patch
mm.patch
mm-allow-gup-to-fail-instead-of-waiting-on-a-page-fix.patch
mm-batch-free-pcp-list-if-possible-fix.patch
frv-duplicate-output_buffer-of-e03-checkpatch-fixes.patch
hpet-factor-timer-allocate-from-open.patch
arch-alpha-include-asm-ioh-s-extern-inline-static-inline.patch
kernel-cpuc-fix-many-errors-related-to-style-fix.patch
epoll-fix-compiler-warning-and-optimize-the-non-blocking-path.patch
lib-hexdumpc-make-hex2bin-return-the-updated-src-address.patch
fs-binfmt_miscc-use-kernels-hex_to_bin-method-fix.patch
fs-binfmt_miscc-use-kernels-hex_to_bin-method-fix-fix.patch
scatterlist-new-helper-functions.patch
crash_dump-export-is_kdump_kernel-to-modules-consolidate-elfcorehdr_addr-setup_elfcorehdr-and-saved_max_pfn-fix.patch
crash_dump-export-is_kdump_kernel-to-modules-consolidate-elfcorehdr_addr-setup_elfcorehdr-and-saved_max_pfn-fix-fix.patch
journal_add_journal_head-debug.patch
slab-leaks3-default-y.patch
put_bh-debug.patch
memblock-add-input-size-checking-to-memblock_find_region.patch
memblock-add-input-size-checking-to-memblock_find_region-fix.patch
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