linux-kernel - Re: [PATCH] powerpc/legacy_serial: Use early

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Date:   Tue, 20 Apr 2021 10:18:42 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>,
        Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hamish Martin <Hamish.Martin@...iedtelesis.co.nz>
Subject: Re: [PATCH] powerpc/legacy_serial: Use early_ioremap()

Hi Chris,

Le 10/08/2020 à 04:01, Chris Packham a écrit :
> 
> On 24/03/20 10:54 am, Chris Packham wrote:
>> Hi Christophe,
>>
>> On Wed, 2020-02-05 at 12:03 +0000, Christophe Leroy wrote:
>>> [    0.000000] ioremap() called early from
>>> find_legacy_serial_ports+0x3cc/0x474. Use early_ioremap() instead
>>>
>> I was just about to dig into this error message and found you patch. I
>> applied it to a v5.5 base.
>>
>>> find_legacy_serial_ports() is called early from setup_arch(), before
>>> paging_init(). vmalloc is not available yet, ioremap shouldn't be
>>> used that early.
>>>
>>> Use early_ioremap() and switch to a regular ioremap() later.
>>>
>>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> On my system (Freescale T2080 SOC) this seems to cause a crash/hang in
>> early boot. Unfortunately because this is affecting the boot console I
>> don't get any earlyprintk output.
> 
> I've been doing a bit more digging into why Christophe's patch didn't
> work for me. I noticed the powerpc specific early_ioremap_range()
> returns addresses around ioremap_bot. Yet the generic early_ioremap()
> uses addresses around FIXADDR_TOP. If I try the following hack I can
> make Christophe's patch work
> 
> diff --git a/arch/powerpc/include/asm/fixmap.h
> b/arch/powerpc/include/asm/fixmap.h
> index 2ef155a3c821..7bc2f3f73c8b 100644
> --- a/arch/powerpc/include/asm/fixmap.h
> +++ b/arch/powerpc/include/asm/fixmap.h
> @@ -27,7 +27,7 @@
>    #include <asm/kasan.h>
>    #define FIXADDR_TOP    (KASAN_SHADOW_START - PAGE_SIZE)
>    #else
> -#define FIXADDR_TOP    ((unsigned long)(-PAGE_SIZE))
> +#define FIXADDR_TOP    (IOREMAP_END - PAGE_SIZE)
>    #endif
> 
>    /*
> 
> I'll admit to being out of my depth. It seems that the generic
> early_ioremap() is not quite correctly plumbed in for powerpc.

Yes that's probably true for PPC64.

I see that on PPC32 I had to implement the following changes in order to enable earlier use of 
early_ioremap()

https://github.com/torvalds/linux/commit/925ac141d106b55acbe112a9272f970631a3c082


I have the problem with QEMU with the ppce500 machine. It will allow me to investigate it a bit further.