linux-kernel - Re: [PATCH 07/16] tools/include: Add io.h stub

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Date:   Sun, 30 Jan 2022 17:53:24 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Karolina Drobnik <karolinadrobnik@...il.com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org, mike.rapoport@...il.com,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 07/16] tools/include: Add io.h stub

On Sun, Jan 30, 2022 at 06:10:00PM +0200, Mike Rapoport wrote:
> On Fri, Jan 28, 2022 at 12:21:59PM +0100, Karolina Drobnik wrote:
> > On Thu, 2022-01-27 at 14:09 +0000, Matthew Wilcox wrote:
> > > On Thu, Jan 27, 2022 at 02:21:25PM +0100, Karolina Drobnik wrote:
> > > > Add a dummy io.h header.
> > > 
> > > Rather begs the question of what memblock.c needs from linux/io.h.
> > > 
> > > Wouldn't it be better to:
> > > 
> > > +++ b/mm/memblock.c
> > > @@ -18,7 +18,6 @@
> > >  #include <linux/memblock.h>
> > > 
> > >  #include <asm/sections.h>
> > > -#include <linux/io.h>
> > > 
> > >  #include "internal.h"
> > > 
> > 
> > That was something I considered in the very beginning, but didn't have
> > a chance to verify it works for all architectures. I can take a look
> > after I'm finished with other v2 changes.
> > 
> > > (allmodconfig on x86-64 builds fine with this; I have not done an
> > > extended sweep of other arches / build options).
> 
> I did a sweep for defconfigs for all arches and all were fine.

Thanks for doing the sweep, Mike.

I think I found a deeper problem which is masked due to our maze of
header files:

include/asm-generic/io.h:#ifndef virt_to_phys
include/asm-generic/io.h:#define virt_to_phys virt_to_phys

so there's an assumption that <asm/io.h> defines virt_to_phys().
You can see that in a number of architectures, eg:

arch/alpha/include/asm/io.h:static inline unsigned long virt_to_phys(volatile void *address)
arch/ia64/include/asm/io.h:#define virt_to_phys virt_to_phys
arch/mips/include/asm/io.h:#define virt_to_phys virt_to_phys
arch/nios2/include/asm/io.h:#define virt_to_phys(vaddr) \
arch/parisc/include/asm/io.h:#define virt_to_phys(a) ((unsigned long)__pa(a))
arch/powerpc/include/asm/io.h:#define virt_to_phys virt_to_phys
arch/sh/include/asm/io.h:#define virt_to_phys(address)  ((unsigned long)(address))
arch/x86/include/asm/io.h:#define virt_to_phys virt_to_phys

That's clearly not the right place to define it.  Two architectures
put it in asm/memory.h:

arch/arm/include/asm/memory.h:#define virt_to_phys virt_to_phys
arch/arm64/include/asm/memory.h:#define virt_to_phys virt_to_phys

then:

arch/m68k/include/asm/virtconvert.h:#define virt_to_phys virt_to_phys
arch/sparc/include/asm/page_32.h:#define virt_to_phys           __pa
arch/sparc/include/asm/page_64.h:#define virt_to_phys __pa

This needs to be properly sorted out, but I don't want to tell Karolina
that's now her job as a prerequisite for merging this patchset; that
would be unfair.

Cc'ing Arnd.  This is the kind of awful mess that he loves fixing ;-)