DISCONTIGMEM suuport on 32 bits MIPS

DISCONTIGMEM suuport on 32 bits MIPS

[Franck]

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

Re: DISCONTIGMEM suuport on 32 bits MIPS

[Ralf Baechle]

On Mon, Sep 26, 2005 at 11:16:27AM +0200, Franck wrote:

> 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...

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.

> 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.

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

  Ralf

Re: DISCONTIGMEM suuport on 32 bits MIPS

[Franck]

Hi Ralf,

2005/9/26, Ralf Baechle <ralf@linux-mips.org>:
> On Mon, Sep 26, 2005 at 11:16:27AM +0200, Franck wrote:
>
> > 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...
>
> 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.
>

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

Re: DISCONTIGMEM suuport on 32 bits MIPS

[Ralf Baechle]

On Mon, Sep 26, 2005 at 02:46:02PM +0200, Franck wrote:

> > 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.
> 
> 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).

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

Re: DISCONTIGMEM suuport on 32 bits MIPS

[Franck]

2005/9/30, Ralf Baechle <ralf@linux-mips.org>:
> On Mon, Sep 26, 2005 at 02:46:02PM +0200, Franck wrote:
>
> > > 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.
> >
> > 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).
>
> 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.
>

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

Re: DISCONTIGMEM suuport on 32 bits MIPS

[Ralf Baechle]

On Fri, Sep 30, 2005 at 02:40:31PM +0200, Franck wrote:

> > > > 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.
> > >
> > > 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).
> >
> > 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.
> >
> 
> 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 ?

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

Re: DISCONTIGMEM suuport on 32 bits MIPS

[Franck]

2005/9/30, Ralf Baechle <ralf@linux-mips.org>:
> On Fri, Sep 30, 2005 at 02:40:31PM +0200, Franck wrote:
>
> > > > > 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.
> > > >
> > > > 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).
> > >
> > > 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.
> > >
> >
> > 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 ?
>
> 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.
>

Ok, I'll do that.

Thanks
--
               Franck