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

[Biju Das]

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@xxxxxxxxxxxxxx>
> >>>>>>> ---
> >>>>>>> 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?

[    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

regards,
 Biju



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