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arm64: sysreg: allow write_sysreg to use XZR 

Currently write_sysreg has to allocate a temporary register to write
zero to a system register, which is unfortunate given that the MSR
instruction accepts XZR as an operand.

Allow XZR to be used when appropriate by fiddling with the assembly
constraints.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Mark Rutland 2016-09-08 13:55:34 +01:00 committed by Will Deacon
parent ee5e41b5f2
commit 7aff4a2dd3
1 changed files with 6 additions and 2 deletions
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8
arch/arm64/include/asm/sysreg.h
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@ -273,10 +273,14 @@ static inline void config_sctlr_el1(u32 clear, u32 set)
__val; \
})
/*
* The "Z" constraint normally means a zero immediate, but when combined with
* the "%x0" template means XZR.
*/
#define write_sysreg(v, r) do { \
u64 __val = (u64)v; \
asm volatile("msr " __stringify(r) ", %0" \
: : "r" (__val)); \
asm volatile("msr " __stringify(r) ", %x0" \
: : "rZ" (__val)); \
} while (0)
#endif