Subject: DISCONTIGMEM suuport on 32 bits MIPS

From: Franck <[email-masked]>
Date: Mon, 26 Sep 2005 11:16:27 +0200

Hi,

I'm working on a port of 32bit MIPS to a custom board with several
large holes in the memory map. I would like to know the status of
discontiguous memory on MIPS. I have noticed that ip27 Kconfig enables
this feature but I don't see any MIPS generic code that handles it...

Has anybody already done this ? If not then I'll try to work out what
needed from the corresponding i386 code, but I'd appreciate any
pointers.

Thanks
--
               Franck

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From: Ralf Baechle <[email-masked]>
Date: Mon, 26 Sep 2005 14:21:14 +0200

> this feature but I don't see any MIPS generic code that handles it...

IP27 currently the only system that absolutely needs discontiguous
memory in order to work at all.  A few other systems could make use of
discontiguous memory to reduce the waste of memory - the family of
Broadcom SB1 based systems comes to mind.

> needed from the corresponding i386 code, but I'd appreciate any

See IP27.  IP27 has one added extra complexity, it's a NUMA system but
you can ignore that.

  Ralf

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From: Franck <[email-masked]>
Date: Mon, 26 Sep 2005 14:46:02 +0200

Hi Ralf,

> Broadcom SB1 based systems comes to mind.

Isn't discontiguous memory common for embedded system as well ? I
thought so...Anyways can we make discontiguous memory thing move into
generic MIPS code so every future needs for that will profit ? I
looked at other arch, and they seem to implement it that way (in
arch/xxx/mm/discontig.c).

Thanks
--
               Franck

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From: Ralf Baechle <[email-masked]>
Date: Fri, 30 Sep 2005 00:50:25 +0100

> arch/xxx/mm/discontig.c).

Yes, that would be a good thing.  There are several platforms that could
make good use of discontiguous memory support such as Broadcom's Sibyte
SoCs with their insanely large hole in the memory map but also others.

  Ralf

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From: Franck <[email-masked]>
Date: Fri, 30 Sep 2005 14:40:31 +0200

> SoCs with their insanely large hole in the memory map but also others.

Ok I'll try to do that soon (maybe in 1 or 2 weeks). I looked at the
ARM's code and I should be able to do the same on MIPS. Should I keep
IP27 data structure and code although ARM's ones seem to be easier to
understand ?

Thanks
--
               Franck

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From: Ralf Baechle <[email-masked]>
Date: Fri, 30 Sep 2005 14:49:00 +0100

> IP27 data structure and code although ARM's ones seem to be easier to

The IP27 code is a little obscure which partly is explained by it's age;
it's been the first NUMA system to be supported in Linux.  After a
quick look the ARM code seems a little to simple to deal with such a
system, so I suggest you take a look at arch/ia64/mm/discontig.c instead.

  Ralf

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From: Franck <[email-masked]>
Date: Fri, 30 Sep 2005 17:35:48 +0200

> system, so I suggest you take a look at arch/ia64/mm/discontig.c instead.

Ok, I'll do that.

Thanks
--
               Franck