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 <[email protected]>
Cc: Marc Zyngier <[email protected]>
Cc: Suzuki K Poulose <[email protected]>
Reviewed-by: Robin Murphy <[email protected]>
Signed-off-by: Mark Rutland <[email protected]>
Signed-off-by: Will Deacon <[email protected]>

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index cc06794b7346bf566b6edbb308e242c6b6d95815..39fed2e56e98148bbdda10c9059396e8c5635119 100644 (file)
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -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