From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Fri, 26 Oct 2012 17:24:44 +0100 Subject: [PATCH] ARM: io: avoid GCC's offsettable addressing modes for halfword accesses Message-ID: <1351268684-20559-1-git-send-email-will.deacon@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Using the 'o' memory constraint in inline assembly can result in GCC generating invalid immediate offsets for memory access instructions with reduced addressing capabilities (i.e. smaller than 12-bit immediate offsets): http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54983 As there is no constraint to specify the exact addressing mode we need, fallback to using 'Q' exclusively for halfword I/O accesses. This may emit an additional add instruction (using an extra register) in order to construct the address but it will always be accepted by GAS. Reported-by: Bastian Hecht Signed-off-by: Will Deacon --- arch/arm/include/asm/io.h | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h index 35c1ed8..42f042e 100644 --- a/arch/arm/include/asm/io.h +++ b/arch/arm/include/asm/io.h @@ -64,7 +64,7 @@ extern void __raw_readsl(const void __iomem *addr, void *data, int longlen); static inline void __raw_writew(u16 val, volatile void __iomem *addr) { asm volatile("strh %1, %0" - : "+Qo" (*(volatile u16 __force *)addr) + : "+Q" (*(volatile u16 __force *)addr) : "r" (val)); } @@ -72,7 +72,7 @@ static inline u16 __raw_readw(const volatile void __iomem *addr) { u16 val; asm volatile("ldrh %1, %0" - : "+Qo" (*(volatile u16 __force *)addr), + : "+Q" (*(volatile u16 __force *)addr), "=r" (val)); return val; } -- 1.7.4.1