Re: [PATCH] powerpc/legacy_serial: Use early_ioremap()

[Christophe Leroy]

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@xxxxxx>
> > 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.