On 27/10/16 13:17, Ding Tianhong wrote: > > > On 2016/10/27 18:58, Marc Zyngier wrote: >> On 27/10/16 08:34, Ding Tianhong wrote: >>> Erratum Hisilicon-161601 says that the ARM generic timer counter "has the >>> potential to contain an erroneous value when 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 the system count registers until the value of the second >>> read is larger than the first one by less than 32, the system counter can be guaranteed >>> not to return wrong value twice by back-to-back read and the error value is always larger >>> than the correct one by 32. Writes to TVAL are replaced with an equivalent write to CVAL. >>> >>> The workaround is enabled if the hisilicon,erratum-161601 property is found in >>> the timer node in the device tree. This can be overridden with the >>> clocksource.arm_arch_timer.hisilicon-161601 boot parameter, which allows KVM >>> users to enable the workaround until a mechanism is implemented to >>> automatically communicate this information. >>> >>> Fix some description for fsl erratum a008585. >>> >>> v2: Significant rework based on feedback, including seperate the fsl erratum a008585 >>> to another patch, update the erratum name and remove unwanted code. >>> >>> Signed-off-by: Ding Tianhong <dingtianhong@xxxxxxxxxx> >>> --- >>> Documentation/arm64/silicon-errata.txt | 1 + >>> Documentation/kernel-parameters.txt | 9 ++++ >>> arch/arm64/include/asm/arch_timer.h | 28 ++++++++++- >>> drivers/clocksource/Kconfig | 14 +++++- >>> drivers/clocksource/arm_arch_timer.c | 88 ++++++++++++++++++++++++++-------- >>> 5 files changed, 118 insertions(+), 22 deletions(-) >>> >>> diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt >>> index 405da11..70c5d5e 100644 >>> --- a/Documentation/arm64/silicon-errata.txt >>> +++ b/Documentation/arm64/silicon-errata.txt >>> @@ -63,3 +63,4 @@ stable kernels. >>> | Cavium | ThunderX SMMUv2 | #27704 | N/A | >>> | | | | | >>> | Freescale/NXP | LS2080A/LS1043A | A-008585 | FSL_ERRATUM_A008585 | >>> +| Hisilicon | Hip05/Hip06/Hip07 | #161601 | HISILICON_ERRATUM_161601| >> >> I've already commented on the alignment. Please read my initial review. >> > > It sees misunderstood, fix it this time. > >>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt >>> index 6fa1d8a..735b4b6 100644 >>> --- a/Documentation/kernel-parameters.txt >>> +++ b/Documentation/kernel-parameters.txt >>> @@ -707,6 +707,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted. >>> erratum. If unspecified, the workaround is >>> enabled based on the device tree. >>> >>> + clocksource.arm_arch_timer.hisilicon-161601= >>> + [ARM64] >>> + Format: <bool> >>> + Enable/disable the workaround of Hisilicon >>> + erratum 161601. 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 >>> diff --git a/arch/arm64/include/asm/arch_timer.h b/arch/arm64/include/asm/arch_timer.h >>> index 118719d8..49b3041 100644 >>> --- a/arch/arm64/include/asm/arch_timer.h >>> +++ b/arch/arm64/include/asm/arch_timer.h >>> @@ -29,7 +29,7 @@ >>> >>> #include <clocksource/arm_arch_timer.h> >>> >>> -#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) >>> +#if IS_ENABLED(CONFIG_FSL_ERRATUM_A008585) || IS_ENABLED(CONFIG_HISILICON_ERRATUM_161601) >>> extern struct static_key_false arch_timer_read_ool_enabled; >>> #define needs_timer_erratum_workaround() \ >>> static_branch_unlikely(&arch_timer_read_ool_enabled) >>> @@ -65,11 +65,35 @@ extern struct arch_timer_erratum_workaround *erratum_workaround; >>> _new; \ >>> }) >>> >>> + >>> + >>> +/* >>> + * The number of retries is an arbitrary value well beyond the highest number >>> + * of iterations the loop has been observed to take. >>> + * Verify whether the value of the second read is larger than the first by >>> + * less than 32 is the only way to confirm the value is correct, the system >>> + * counter can be guaranteed not to return wrong value twice by back-to-back read >>> + * and the error value is always larger than the correct one by 32. >>> + */ >>> +#define __hisi_161601_read_reg(reg) ({ \ >>> + u64 _old, _new; \ >>> + int _retries = 200; \ >> >> Please document how this value was found (either in the code or in the >> commit message). > > It really difficult to give the accurate standard, theoretically the error should not happened > twice together, so maybe 2 is enough here, I just give a arbitrary value. > >> >>> + \ >>> + do { \ >>> + _old = read_sysreg(reg); \ >>> + _new = read_sysreg(reg); \ >>> + _retries--; \ >>> + } while (unlikely((_new - _old) >> 5) && _retries); \ >>> + \ >>> + WARN_ON_ONCE(!_retries); \ >>> + _new; \ >>> +}) >> >> Same remark as in the previous patch. >> > > I think the sentence *Verify whether the value of the second read is larger than the first by > less than 32 is the only way to confirm the value is correct* could explain why should *(_new - _old) >> 5*. > it is the same as (_new - _old)/32, also mean the _new should never bigger than _old more than 32. This is not about the explanation of the erratum, but about the location of the #define, which can be made private to the .c file instead of being globally visible. Thanks, M. -- Jazz is not dead. It just smells funny... -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html