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

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Date:   Sat, 16 Nov 2019 10:49:32 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     "kernelci.org bot" <bot@...nelci.org>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ardb@...nel.org>, tomeu.vizoso@...labora.com,
        Guillaume Tucker <guillaume.tucker@...labora.com>,
        mgalka@...labora.com, Mark Brown <broonie@...nel.org>,
        Matt Hart <matthew.hart@...aro.org>,
        Kevin Hilman <khilman@...libre.com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Marc Zyngier <maz@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stefan Agner <stefan@...er.ch>,
        Nicolas Pitre <nico@...xnic.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: rmk/for-next bisection: boot on
 ox820-cloudengines-pogoplug-series-3

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@...nelci.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@...nelci.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.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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