From mboxrd@z Thu Jan 1 00:00:00 1970 From: akpm@linux-foundation.org Subject: [patch 1/4] arch/x86/include/asm/delay.h: fix udelay() and ndelay() for 8-bit args Date: Mon, 23 May 2011 14:47:00 -0700 Message-ID: <201105232147.p4NLl0ti013960@imap1.linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Return-path: Received: from smtp1.linux-foundation.org ([140.211.169.13]:36732 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757651Ab1EWVrU (ORCPT ); Mon, 23 May 2011 17:47:20 -0400 Sender: linux-arch-owner@vger.kernel.org List-ID: To: mingo@elte.hu Cc: hpa@zytor.com, tglx@linutronix.de, akpm@linux-foundation.org, linux-arch@vger.kernel.org From: Andrew Morton 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 Cc: Thomas Gleixner Cc: "H. Peter Anvin" Cc: Signed-off-by: Andrew Morton --- 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); _