Re: rmk/for-next bisection: boot on ox820-cloudengines-pogoplug-series-3

From: Russell King - ARM Linux admin
Date: Sat Nov 16 2019 - 05:50:37 EST


On Sat, Nov 16, 2019 at 10:26:27AM +0000, Ard Biesheuvel wrote:
> (+ Arnd)
>
> On Sat, 16 Nov 2019 at 05:54, kernelci.org bot <bot@xxxxxxxxxxxx> wrote:
> >
> > * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
> > * This automated bisection report was sent to you on the basis *
> > * that you may be involved with the breaking commit it has *
> > * found. No manual investigation has been done to verify it, *
> > * and the root cause of the problem may be somewhere else. *
> > * *
> > * If you do send a fix, please include this trailer: *
> > * Reported-by: "kernelci.org bot" <bot@xxxxxxxxxxxx> *
> > * *
> > * Hope this helps! *
> > * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
> >
> > rmk/for-next bisection: boot on ox820-cloudengines-pogoplug-series-3
> >
> > Summary:
> > Start: b6c3c42cfda0 ARM: 8938/1: kernel: initialize broadcast hrtimer based clock event device
> > Details: https://kernelci.org/boot/id/5dcf3f0359b514dc84cf54c8
> > Plain log: https://storage.kernelci.org//rmk/for-next/v5.4-rc5-26-gb6c3c42cfda0/arm/oxnas_v6_defconfig/gcc-8/lab-baylibre/boot-ox820-cloudengines-pogoplug-series-3.txt
> > HTML log: https://storage.kernelci.org//rmk/for-next/v5.4-rc5-26-gb6c3c42cfda0/arm/oxnas_v6_defconfig/gcc-8/lab-baylibre/boot-ox820-cloudengines-pogoplug-series-3.html
> > Result: ea70bf6e92c5 ARM: 8935/1: decompressor: avoid CP15 barrier instructions in v7 cache setup code
> >
>
> OK, so this regression is caused by the fact that the 'armv7' cache
> maintenance routines in the decompressor are also used for ARMv6 cores
> if they implement the CPUID extension, which I failed to realise when
> I sent this patch.
>
> There are roughly three ways to deal with this:
> 1) add a mask/val match pair for ARM11MPcore and ARM1176 that hardwire
> them to the ARMv6 routines, even though they implement the CPUID
> extension. This would be very easy, but assumes that those two cores
> are the only ones that are affected by this.
> 2) modify the v7 routines to check for the L1Hvd MMFR1 attribute (in
> the flush routine) and for the CP15BEN SCTLR bit (in the on/off
> routines), and jump to the respective v6 variants if the CPU turns out
> not to support the v7 one.
> 3) revert the patch, and just enable the CP15 barriers (and issue a v7
> barrier) in the v7 on() and flush() routines.
>
> I am leaning towards the latter, since it is the most straightforward,
> even though it mixes v7 and cp15 barriers in the same function, but
> that was mostly a cosmetic concern anyway.

I'm going to drop the patches - if -rc8 is released tomorrow maybe we
can have a go at solving it next week.

--
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