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

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Date:   Sun, 24 Apr 2022 08:28:19 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Arnd Bergmann <arnd@...nel.org>
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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Subject: Re: [PATCH v2 00/48] ARM: PXA multiplatform support

On 4/24/22 01:52, Arnd Bergmann wrote:
> 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.
> 

Yes, that works. I changed it in my configuration.

>>> 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.

Guenter