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clocksource/arm_arch_timer: Improve Allwinner A64 timer workaround
commit8b33dfe0ba
upstream. 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:c950ca8c35
("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 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -348,7 +348,7 @@ static u64 notrace arm64_858921_read_cntvct_el0(void)
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do { \
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_val = read_sysreg(reg); \
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_retries--; \
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} while (((_val + 1) & GENMASK(9, 0)) <= 1 && _retries); \
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} while (((_val + 1) & GENMASK(8, 0)) <= 1 && _retries); \
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\
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WARN_ON_ONCE(!_retries); \
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_val; \
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