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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Sun, 24 Apr 2022 20:48:39 +0200
Message-ID: <CAK8P3a2EHMQPN4ny9sXXuReFG0jN0hyRV7h9v_AR_0pqpOU41w@mail.gmail.com>
Subject: Re: [PATCH v2 00/48] ARM: PXA multiplatform support
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     Robert Jarzmik <robert.jarzmik@free.fr>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Arnd Bergmann <arnd@arndb.de>, Daniel Mack <daniel@zonque.org>,
        Haojian Zhuang <haojian.zhuang@gmail.com>,
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On Sun, Apr 24, 2022 at 5:28 PM Guenter Roeck <linux@roeck-us.net> wrote:
> On 4/24/22 01:52, Arnd Bergmann wrote:
> > On Sun, Apr 24, 2022 at 4:09 AM Guenter Roeck <linux@roeck-us.net> wrote:
> > 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.
> >
>
> Yes, that works. I changed it in my configuration.

Ok, great!. I managed to boot the z2 machine with PCMCIA support
and it gets around the issue with my patch, correctly detecting the
CF card.

> >>> 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.
> >
>
> That looks like a bug in qemu. ARM925T instruction support is limited to V4T
> instructions. qemu doesn't have explicit 5T support. It is either V4T
> or V5.

I'm not entirely sure what instructions the CPU supports, but Linux
treats it as ARMv4T as well, and qemu supports some of the 925t
specific instructions as "ti925t" in target/arm/cpu_tcg.c, it just seems
it's missing some others.

      Arnd