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 <20191116104932.GT25745@shell.armlinux.org.uk>
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From:   Ard Biesheuvel <ard.biesheuvel@linaro.org>
Date:   Sat, 16 Nov 2019 16:35:53 +0100
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Subject: Re: rmk/for-next bisection: boot on ox820-cloudengines-pogoplug-series-3
To:     Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc:     "kernelci.org bot" <bot@kernelci.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Ard Biesheuvel <ardb@kernel.org>, tomeu.vizoso@collabora.com,
        Guillaume Tucker <guillaume.tucker@collabora.com>,
        mgalka@collabora.com, Mark Brown <broonie@kernel.org>,
        Matt Hart <matthew.hart@linaro.org>,
        Kevin Hilman <khilman@baylibre.com>,
        Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        Marc Zyngier <maz@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Stefan Agner <stefan@agner.ch>,
        Nicolas Pitre <nico@fluxnic.net>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
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On Sat, 16 Nov 2019 at 11:49, Russell King - ARM Linux admin
<linux@armlinux.org.uk> wrote:
>
> 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@kernelci.org> 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@kernelci.org>          *
> > > *                                                               *
> > > * 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.
>

Fair enough.