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

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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>
This commit is contained in:
Will Deacon 2012-10-26 18:42:08 +01:00 committed by Russell King
parent 39141ddfb6
commit 7629a9f661
1 changed files with 2 additions and 2 deletions
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4
arch/arm/include/asm/io.h
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@ -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;
}