linux-kernel - Re: [PATCH 00/17] clocksource/arch_timer: Errara workaround infrastructure rework

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Date:   Mon, 6 Mar 2017 14:48:50 -0700
From:   dann frazier <dann.frazier@...onical.com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Scott Wood <oss@...error.net>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Ding Tianhong <dingtianhong@...wei.com>
Subject: Re: [PATCH 00/17] clocksource/arch_timer: Errara workaround
 infrastructure rework

On Mon, Mar 6, 2017 at 4:26 AM, Marc Zyngier <marc.zyngier@....com> wrote:
> It has recently become obvious that a number of arm64 systems have
> been blessed with a set of timers that are slightly less than perfect,
> and require a bit of hand-holding. We already have a bunch of
> errata-specific code to deal with this, but as we're adding more
> potential detection methods (DT, ACPI, capability), things are getting
> a bit out of hands.
>
> Instead of adding more ad-hoc fixes to an already difficult code base,
> let's give ourselves a bit of an infrastructure that can deal with
> this and hide most of the uggliness behind frendly accessors.
>
> The series is structured as such:
>
> - The first half of the series rework the existing workarounds,
>   allowing errata to be matched using a given detection method
>
> - Another patch allows a workaround to affect a subset of the CPUs,
>   and not the whole system
>
> - Another set of patches allow the virtual counter to be trapped when
>   accessed from userspace (something that affects the current set of
>   broken platform, and that is not worked around yet)
>
> - We then work around a Cortex-A73 erratum, whose counter can return a
>   wrong value if read while crossing a 32bit boundary
>
> - Finally, we add some ACPI-specific workarounds for HiSilicon
>   platforms that have the HISILICON_ERRATUM_161010101 defect.
>
> Note that so far, we only deal with arm64. Once the infrastructure is
> agreed upon, we can look at generalizing it (to some extent) to 32bit
> ARM (typical use case would be a 32bit guest running on an affected
> host).

Thanks Marc. Worked on our HiSilicon board:

[    0.000000] arm_arch_timer: Enabling global workaround for
HiSilicon erratum 161010101
[    0.000000] arm_arch_timer: CPU0: Trapping CNTVCT access
[    0.000000] arm_arch_timer: Architected cp15 timer(s) running at
50.00MHz (phys).
[    0.266571] arm_arch_timer: CPU1: Trapping CNTVCT access
[    0.270108] arm_arch_timer: CPU2: Trapping CNTVCT access
[...]

Tested-by: dann frazier <dann.frazier@...onical.com>

  -dann