Re: [PATCH] arm64: dts: renesas: r8a7796: Add CMT device nodes

[Daniel Lezcano <daniel.lezcano@linaro.org>]

Added Marc Zyngier in Cc.

On 22/11/2018 16:16, Biju Das wrote:
> Hello Daniel,
> 
> Thanks for the feedback.
> 
>>>> Subject: Re: [PATCH] arm64: dts: renesas: r8a7796: Add CMT device
>>>> nodes
>>>>
>>>> On 19/11/2018 16:50, Biju Das wrote:
>>>>> Hi Daniel,
>>>>>
>>>>> Thanks for the feedback.
>>>>>
>>>>>>>> Subject: Re: [PATCH] arm64: dts: renesas: r8a7796: Add CMT device
>>>>>>>> nodes
>>>>>>>>
>>>>>>>> On 26/10/2018 10:25, Biju Das wrote:
>>>>>>>>> This patch adds CMT{0|1|2|3} device nodes for r8a7796 SoC.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Biju Das <biju.das@bp.renesas.com>
>>>>>>>>> ---
>>>>>>>>> This patch is tested against renesas-dev
>>>>>>>>>
>>>>>>>>> I have executed on inconsistency-check, nanosleep and
>>>>>>>>> clocksource_switch selftests on this arm64 SoC. The
>>>>>>>>> inconsistency-check and nanosleep tests are working fine.The
>>>>>>>>> clocksource_switch asynchronous test is failing due to
>>>>>>>>> inconsistency-check
>>>>>>>> failure on "arch_sys_counter".
>>>>>>>>>
>>>>>>>>> But if i skip the clocksource_switching of "arch_sys_counter",
>>>>>>>>> the asynchronous test is passing for CMT0/1/2/3 timer.
>>>>>>>>>
>>>>>>>>> Has any one noticed this issue?
>>>>>>>>
>>>>>>>> So now that you mention that, I've been through the
>>>>>>>> clocksource_switch on another ARM64 platform (hikey960) and
>>>>>>>> disabled the
>>>>>>>> ARM64_ERRATUM_858921 config option. I can see the same issue.
>>>>>>>>
>>>>>>>> Is this option set on your config ?
>>>>>>>
>>>>>>> No.  As per  " config ARM64_ERRATUM_858921", it is "Workaround for
>>>>>> Cortex-A73 erratum 858921"
>>>>>>>
>>>>>>> Our SoC is 2xCA-57 + 4 x CA-53.  Does  it impact CA-57 + CA_53?
>>>>>>
>>>>>> Dunno :/
>>>>>>
>>>>>>> Any way I will enable this config option and will provide you the
>> results.
>>>>>>
>>>>>> Ok, thanks!
>>>>>
>>>>> The following config is enabled by default on upstream
>>>>> kernel(4.20-rc3) CONFIG_ARM_ARCH_TIMER_EVTSTREAM=y
>>>>> CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND=y
>>>>> CONFIG_FSL_ERRATUM_A008585=y
>>>>> CONFIG_HISILICON_ERRATUM_161010101=y
>>>>> CONFIG_ARM64_ERRATUM_858921=y
>>>>>
>>>>> For a quick testing,  I have activated the erratum using the
>>>>> property
>>>> "fsl,erratum-a008585" on device tree.
>>>>> With this I confirm the issue is fixed.
>>>>>
>>>>> I have  some questions on this.
>>>>> 1) Based  on the test result ,do you think renesas soc also
>>>>> impacted by the
>>>> ARM64_ERRATUM_858921?
>>>>> 2) Is there any way to find, is this Erratum actually causing the
>>>> asynchronous test to fail?
>>>>
>>>> I guess, you can hack the __fsl_a008585_read_reg macro and check if
>>>> the invalid condition is reached.
>>>>
>>>> This thread https://lkml.org/lkml/2018/5/10/773 will give you all the
>>>> answers you are looking for (well very likely).
>>>>
>>>> Let me know if it helped.
>>>
>>> In our case , Delta: 174760 ns
>>>
>>> 1530553351:205762284
>>> 1530553351:205762404
>>> --------------------
>>> 1530553351:205951226
>>> 1530553351:205776466
>>> --------------------
>>>
>>> I have tried the workaround for ARM64_ERRATUM_858921, that also fixes
>> the issue.
>>>
>>> But all the workaround disables ARM64 VDSO. How do we conclude that is
>> it VDSO issue or ARM64_ERRATUM issue?
>>
>> May be disable all errata and set vdso_default to false?
>>
>> [ ... ]
>>
>> -static bool vdso_default = true;
>> +static bool vdso_default = false;
>>
>> [ ... ]
> 
> I have disabled the  activation of errata from device tree and set vdso_default=false.
> With this also it works fine. So looks like arm64 vdso is the issue in our case.
> 
> Do you agree with the conclusion?

I agree we have an element to investigate the issue. That is very
specific to this timer and a good knowledge of the internals is required.

Certainly Marc Zyngier or Mark Rutland can help here.

> [    0.000000] rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=6
> [    0.000000] NR_IRQS: 64, nr_irqs: 64, preallocated irqs: 0
> [    0.000000] arch_timer: cp15 timer(s) running at 8.32MHz (virt).
> [    0.000000] clocksource: arch_sys_counter: mask: 0xffffffffffffff max_cycles: 0x1eb398c07, max_idle_ns: 440795202503 ns
> [    0.000004] sched_clock: 56 bits at 8MHz, resolution 120ns, wraps every 2199023255503ns



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