From 8b33dfe0ba1c84c1aab2456590b38195837f1e6e Mon Sep 17 00:00:00 2001
From: Samuel Holland <samuel@sholland.org>
Date: Fri, 14 May 2021 21:14:39 -0500
Subject: [PATCH] clocksource/arm_arch_timer: Improve Allwinner A64 timer workaround
Git-commit: 8b33dfe0ba1c84c1aab2456590b38195837f1e6e
Patch-mainline: v5.14-rc1
References: git-fixes

Bad counter reads are experienced sometimes when bit 10 or greater rolls
over. Originally, testing showed that at least 10 lower bits would be
set to the same value during these bad reads. However, some users still
reported time skips.

Wider testing revealed that on some chips, occasionally only the lowest
9 bits would read as the anomalous value. During these reads (which
still happen only when bit 10), bit 9 would read as the correct value.

Reduce the mask by one bit to cover these cases as well.

Cc: stable@vger.kernel.org
Fixes: c950ca8c35ee ("clocksource/drivers/arch_timer: Workaround for Allwinner A64 timer instability")
Reported-by: Roman Stratiienko <r.stratiienko@gmail.com>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210515021439.55316-1-samuel@sholland.org
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/clocksource/arm_arch_timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 89a9e0524555..be6d741d404c 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -364,7 +364,7 @@ static u64 notrace arm64_858921_read_cntvct_el0(void)
 	do {								\
 		_val = read_sysreg(reg);				\
 		_retries--;						\
-	} while (((_val + 1) & GENMASK(9, 0)) <= 1 && _retries);	\
+	} while (((_val + 1) & GENMASK(8, 0)) <= 1 && _retries);	\
 									\
 	WARN_ON_ONCE(!_retries);					\
 	_val;								\
-- 
2.26.2