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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Niklas Schnelle' <schnelle@linux.ibm.com>,
        Arnd Bergmann <arnd@arndb.de>
CC:     Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        "clang-built-linux@googlegroups.com" 
        <clang-built-linux@googlegroups.com>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>
Subject: RE: [PATCH v2 1/2] sparc: explicitly set PCI_IOBASE to 0
Thread-Topic: [PATCH v2 1/2] sparc: explicitly set PCI_IOBASE to 0
Thread-Index: AQHXMfQU/v+fCAtEaUGryS2VPWnQoKq1vegA
Date:   Thu, 15 Apr 2021 16:10:33 +0000
Message-ID: <af5f3d8390654abda295860c756cb687@AcuMS.aculab.com>
References: <20210415123700.3030728-1-schnelle@linux.ibm.com>
 <20210415123700.3030728-2-schnelle@linux.ibm.com>
In-Reply-To: <20210415123700.3030728-2-schnelle@linux.ibm.com>
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From: Niklas Schnelle
> Sent: 15 April 2021 13:37
> 
> Instead of relying on the fallback in asm-generic/io.h which sets
> PCI_IOBASE 0 if it is not defined set it explicitly.
> 
> Link: https://lore.kernel.org/lkml/CAK8P3a3PK9zyeP4ymELtc2ZYnymECoACiigw9Za+pvSJpCk5=g@mail.gmail.com/
> Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
> ---
>  arch/sparc/include/asm/io.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/sparc/include/asm/io.h b/arch/sparc/include/asm/io.h
> index 2eefa526b38f..100992ba1317 100644
> --- a/arch/sparc/include/asm/io.h
> +++ b/arch/sparc/include/asm/io.h
> @@ -1,6 +1,10 @@
>  /* SPDX-License-Identifier: GPL-2.0 */
>  #ifndef ___ASM_SPARC_IO_H
>  #define ___ASM_SPARC_IO_H
> +
> +/* On LEON I/O Space is accessed through low iomem */
> +#define PCI_IOBASE ((void __iomem *)0)
> +
>  #if defined(__sparc__) && defined(__arch64__)
>  #include <asm/io_64.h>
>  #else
> --
> 2.25.1

Not sure the comment is informative enough.
Maybe something like:

/*
 * On LEON PCI addresses below 64k are converted to IO accesses.
 * io_remap_xxx() (whatever is it called) returns a kernel virtual
 * address in the PCI window so inb() doesn't need to add an offset.
 */

That'll save the next person doing a lot of digging.

	David

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