linux-kernel - Re: [PATCH v2 00/48] ARM: PXA multiplatform support

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Date:   Sun, 24 Apr 2022 10:52:36 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Robert Jarzmik <robert.jarzmik@...e.fr>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Arnd Bergmann <arnd@...db.de>, Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Philipp Zabel <philipp.zabel@...il.com>,
        Lubomir Rintel <lkundrak@...sk>,
        Paul Parsons <lost.distance@...oo.com>,
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        Viresh Kumar <viresh.kumar@...aro.org>,
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Subject: Re: [PATCH v2 00/48] ARM: PXA multiplatform support

On Sun, Apr 24, 2022 at 4:09 AM Guenter Roeck <linux@...ck-us.net> wrote:
> On 4/23/22 12:55, Arnd Bergmann wrote:
> > On Sat, Apr 23, 2022 at 1:41 AM Guenter Roeck <linux@...ck-us.net> wrote:
> >> On Sat, Apr 23, 2022 at 12:04:31AM +0200, Arnd Bergmann wrote:
> >
> > Odd, I can't reproduce this at all. Do you get any console output at
> > all for this?
> >
> > Is this the plain omap1_defconfig, or something else?
> >
>
> No, it is my own sx1 specific configuration.
>
> https://github.com/groeck/linux-build-test/blob/master/rootfs/arm/qemu_sx1_defconfig
>
> I don't recall where I got it from but ...

Ok, that explains it, thanks!

I fixed all the defconfig files that come with the kernel, but for your own
ones you have to add

# CONFIG_ARCH_MULTI_V7 is not set

into the defconfig file, otherwise the multiplatform target defaults to
an ARMv7 instead of ARMv5 build. For an OMAP15xx as in the SX1,
you also need to enable CONFIG_ARCH_MULTI_V4T.

This is slightly unfortunate, but I don't see any way to avoid it, and the
modified defconfig will still work fine with older kernel trees.

> > One thing I keep having to apply myself is this snippet:
> >
> > diff --git a/arch/arm/mm/proc-arm925.S b/arch/arm/mm/proc-arm925.S
> > index 0bfad62ea858..87c695703580 100644
> > --- a/arch/arm/mm/proc-arm925.S
> > +++ b/arch/arm/mm/proc-arm925.S
> > @@ -441,7 +441,6 @@ __arm925_setup:
> >
> >   #ifdef CONFIG_CPU_DCACHE_WRITETHROUGH
> >          mov     r0, #4                          @ disable write-back
> > on caches explicitly
> > -       mcr     p15, 7, r0, c15, c0, 0
> >   #endif
>
> it does not have CONFIG_CPU_DCACHE_WRITETHROUGH enabled.

Maybe it was disabled explicitly for the sx1_defconfig because of this
bug. I would think that this is required for actual sx1 hardware because the
option is default-enabled for ARM925T, and that CPU core is exclusively
used in OMAP15xx.

        Arnd