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| author | Scott Wood <oss@buserror.net> | 2016-09-22 10:35:17 +0200 |
|---|---|---|
| committer | Will Deacon <will.deacon@arm.com> | 2016-09-23 18:19:25 +0200 |
| commit | f6dc1576cd517440313c9551b6ffa3d7e389c7c7 (patch) | |
| tree | b8b7e96634c2df9b8de85b5bb80923c2b6aeae97 /Documentation/kernel-parameters.txt | |
| parent | arm64: arch_timer: Add device tree binding for A-008585 erratum (diff) | |
| download | linux-f6dc1576cd517440313c9551b6ffa3d7e389c7c7.tar.xz linux-f6dc1576cd517440313c9551b6ffa3d7e389c7c7.zip | |
arm64: arch_timer: Work around QorIQ Erratum A-008585
Erratum A-008585 says that the ARM generic timer counter "has the
potential to contain an erroneous value for a small number of core
clock cycles every time the timer value changes". Accesses to TVAL
(both read and write) are also affected due to the implicit counter
read. Accesses to CVAL are not affected.
The workaround is to reread TVAL and count registers until successive
reads return the same value. Writes to TVAL are replaced with an
equivalent write to CVAL.
The workaround is to reread TVAL and count registers until successive reads
return the same value, and when writing TVAL to retry until counter
reads before and after the write return the same value.
The workaround is enabled if the fsl,erratum-a008585 property is found in
the timer node in the device tree. This can be overridden with the
clocksource.arm_arch_timer.fsl-a008585 boot parameter, which allows KVM
users to enable the workaround until a mechanism is implemented to
automatically communicate this information.
This erratum can be found on LS1043A and LS2080A.
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Scott Wood <oss@buserror.net>
[will: renamed read macro to reflect that it's not usually unstable]
Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'Documentation/kernel-parameters.txt')
| -rw-r--r-- | Documentation/kernel-parameters.txt | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 46c030a49186..fb4de4daba1f 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -698,6 +698,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted. loops can be debugged more effectively on production systems. + clocksource.arm_arch_timer.fsl-a008585= + [ARM64] + Format: <bool> + Enable/disable the workaround of Freescale/NXP + erratum A-008585. This can be useful for KVM + guests, if the guest device tree doesn't show the + erratum. If unspecified, the workaround is + enabled based on the device tree. + clearcpuid=BITNUM [X86] Disable CPUID feature X for the kernel. See arch/x86/include/asm/cpufeatures.h for the valid bit |