On 2016/10/29 0:00, Will Deacon wrote:
> Hi Ding,
>
> On Thu, Oct 27, 2016 at 03:34:10PM +0800, 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>
>> ---
>
> [...]
>
>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
>> index 8a753fd..4aafb6a 100644
>> --- a/drivers/clocksource/Kconfig
>> +++ b/drivers/clocksource/Kconfig
>> @@ -312,8 +312,20 @@ config FSL_ERRATUM_A008585
>> help
>> This option enables a workaround for Freescale/NXP Erratum
>> A-008585 ("ARM generic timer may contain an erroneous
>> - value"). The workaround will only be active if the
>> + value"). The workaround will be active if the
>> fsl,erratum-a008585 property is found in the timer node.
>> + This can be overridden with the clocksource.arm_arch_timer.fsl-a008585
>> + boot parameter.
>> +
>> +config HISILICON_ERRATUM_161601
>> + bool "Workaround for Hisilicon Erratum 161601"
>> + default y
>> + depends on ARM_ARCH_TIMER && ARM64
>> + help
>> + This option enables a workaround for Hisilicon Erratum
>> + 161601. The workaround will be active if the hisilicon,erratum-161601
>> + property is found in the timer node. This can be overridden with
>> + the clocksource.arm_arch_timer.hisilicon-161601 boot parameter.
>
> I'm really not keen on having a kernel commandline parameter for this.
> It's not something we've done for other, similar errata (e.g. CNTFRQ
> reporting the wrong value) and I think it's a slippery slope to having
> more of these workarounds controlled at boot-time. If you have a board
> that is affected by this, it's always going to need the workaround. Why
> would you turn it off?
>
OK, miss it.
> Will
>
> .
>
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