On 2016/10/27 20:23, Marc Zyngier wrote:
> 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.
>
Ok, update it .
Thanks
Ding
> Thanks,
>
> M.
>
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