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Re: Proposal: non-PC ISA bus support

To: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Subject: Re: Proposal: non-PC ISA bus support
From: Frank Rowand <frank_rowand@mvista.com>
Date: Tue, 20 Jun 2000 10:11:45 -0700
Cc: Linux kernel <linux-kernel@vger.rutgers.edu>, Linux/PPC Development <linuxppc-dev@lists.linuxppc.org>, Linux/MIPS Development <linux@cthulhu.engr.sgi.com>
Organization: Montavista Software, Inc
References: <Pine.GSO.4.10.10006201254290.8592-100000@dandelion.sonytel.be>
Reply-to: frowand@mvista.com
Sender: owner-linux-mips@oss.sgi.com
Geert Uytterhoeven wrote:
> 
> The following patch fixes 2 problems related to ISA bus access on non-PC
> platforms:
> 
>  1. ISA I/O space is memory mapped on many platforms (e.g. PPC and MIPS). To
>     access it from user space, you cannot plainly use inb() and friends like 
> on
>     PC, but you have to mmap() the correct region of /dev/mem first. This
>     region depends on the machine type and currently there's no simple way to
>     find out from user space.
> 
>  2. ISA memory is not located at physical address 0 on many platforms (e.g. 
> PPC
>     and some MIPS boxes). This means you cannot e.g. use
>     request_mem_region(0xa0000, 65536) to request the legacy VGA region.
> 
> Solutions:
> 
>  1. Provide /proc/bus/isa/map, which contains the ISA I/O and memory space
>     mappings on machines where these are memory mapped.
> 
>     Example (on PPC CHRP LongTrail):
> 
>         callisto$ cat /proc/bus/isa/map
>         f8000000        01000000        IO
>         f7000000        01000000        MEM
>         callisto$
> 
>     The region marked `IO' is ISA (also PCI) I/O space, while the region 
> marked
>     `MEM' is ISA memory space. Of course on a PC the first one is not
>     available because there are separate I/O and memory spaces on ia32.
> 
>  2. Provide new resource management functions for ISA memory space:
> 
>         isa_request_mem_region()
>         isa_check_mem_region()
>         isa_release_mem_region()
> 
>     On ia32, these are identical to the normal memory resource management
>     functions.
> 
>     [ Alternatively we could add tests to the *_mem_region() functions to test
>       whether the requested region is < 16 MB (and thus in ISA memory space)
>       and add the required offset. But this affects the common resource code
>       and may cause problems on machines where there is no ISA space in the
>       first 16 MB of memory space. ]
> 
> The patch contains support for ia32, PPC and MIPS (limited to DDB Vrc-5074).
> It was tested on PPC only.
> 
> Comments are welcomed!

Would it make sense to apply the same sort of fix to the following code in
__ioremap(), so that ISA space is handled consistently?:

        /*
         * If the address lies within the first 16 MB, assume it's in ISA
         * memory space
         */
        if (p < 16*1024*1024)
            p += _ISA_MEM_BASE;


< patch deleted >


> 
> Gr{oetje,eeting}s,
> 
>                                                 Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- 
> geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like 
> that.
>                                                             -- Linus Torvalds
> 
> ** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/

-Frank
-- 
Frank Rowand <frank_rowand@mvista.com>
MontaVista Software, Inc

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