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Subject[PATCH] arm64/io: Don't use WZR in writel
From 33fb6d036de273bb71ac1c67d7a91b7a5148e659 Mon Sep 17 00:00:00 2001
From: "Angelo G. Del Regno" <>
Date: Sat, 9 Feb 2019 18:56:46 +0100
Subject: [PATCH] arm64/io: Don't use WZR in writel

This is a partial revert of commit ee5e41b5f21a
("arm64/io: Allow I/O writes to use {W,X}ZR")

When we try to use the zero register directly on some SoCs,
their security will make them freeze due to a firmware bug.
This behavior is seen with the arm-smmu driver freezing on
TLBI and TLBSYNC on MSM8996, MSM8998, SDM630, SDM660.

Allocating a temporary register to store the zero for the
write actually solves the issue on these SoCs.

Signed-off-by: Angelo G. Del Regno <>
arch/arm64/include/asm/io.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
index ee723835c1f4..a0a6d1aeb670 100644
--- a/arch/arm64/include/asm/io.h
+++ b/arch/arm64/include/asm/io.h
@@ -49,7 +49,7 @@ static inline void __raw_writew(u16 val, volatile void __iomem *addr)
#define __raw_writel __raw_writel
static inline void __raw_writel(u32 val, volatile void __iomem *addr)
- asm volatile("str %w0, [%1]" : : "rZ" (val), "r" (addr));
+ asm volatile("str %w0, [%1]" : : "r" (val), "r" (addr));

#define __raw_writeq __raw_writeq

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