ARM: 7567/1: io: avoid GCC's offsettable addressing modes for halfword accesses

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 <hechtb@googlemail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h
index 35c1ed8..42f042e 100644 (file)
--- 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;
 }