[PATCH 1/2] arm64: tlb: Allow XZR argument to TLBI ops

[Mark Rutland]

The TLBI instruction accepts XZR as a register argument, and for TLBI
operations with a register argument, there is no functional difference
between using XZR or another GPR which contains zeroes. Operations
without a register argument are encoded as if XZR were used.

Allow the __TLBI_1() macro to use XZR when a register argument is all
zeroes.

Today this only results in a trivial code saving in
__do_compat_cache_op()'s workaround for Neoverse-N1 erratum #1542419. In
subsequent patches this pattern will be used more generally.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Oliver Upton <oupton at kernel.org>
Cc: Ryan Roberts <ryan.roberts at arm.com>
Cc: Will Deacon <will at kernel.org>
---
 arch/arm64/include/asm/tlbflush.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
index a2d65d7d6aaeb..bf1cc9949dc87 100644
--- a/arch/arm64/include/asm/tlbflush.h
+++ b/arch/arm64/include/asm/tlbflush.h
@@ -38,12 +38,12 @@
 			    : : )
 
 #define __TLBI_1(op, arg) asm (ARM64_ASM_PREAMBLE			       \
-			       "tlbi " #op ", %0\n"			       \
+			       "tlbi " #op ", %x0\n"			       \
 		   ALTERNATIVE("nop\n			nop",		       \
-			       "dsb ish\n		tlbi " #op ", %0",     \
+			       "dsb ish\n		tlbi " #op ", %x0",    \
 			       ARM64_WORKAROUND_REPEAT_TLBI,		       \
 			       CONFIG_ARM64_WORKAROUND_REPEAT_TLBI)	       \
-			    : : "r" (arg))
+			    : : "rZ" (arg))
 
 #define __TLBI_N(op, arg, n, ...) __TLBI_##n(op, arg)
 
-- 
2.30.2