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authorScott Wood <oss@buserror.net>2016-09-22 03:35:17 -0500
committerWill Deacon <will.deacon@arm.com>2016-09-23 17:19:25 +0100
commitf6dc1576cd517440313c9551b6ffa3d7e389c7c7 (patch)
treeb8b7e96634c2df9b8de85b5bb80923c2b6aeae97 /Documentation/kernel-parameters.txt
parent22e43390456152f6e72ad2632e2b3fb363e94146 (diff)
downloadlinux-aarch64-f6dc1576cd517440313c9551b6ffa3d7e389c7c7.tar.gz
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.txt9
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