how to support more than 512MB RAM for MIPS32 ?

how to support more than 512MB RAM for MIPS32 ?

[figo zhang]

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hi all,

I am using 24KEC SOC, i want to support larger more than 512MB RAM. The
mips32 architure  in Kseg0/Kseg1,
such as:
0x8000,0000 ~ 0x92c0,0000  # 300MB for RAM
0x92c0,0000 ~ 0xa000,0000  # 212 for I/O register

so, mips32 only support 300MB memory, i dont how to support more than 512MB
in linux-mips kernel , such as 2GB memory? it is using HIGHMEM strategy
for kernel(ZONE_HIGHMEM)?

Best,
Figo.zhang

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Re: how to support more than 512MB RAM for MIPS32 ?

[Kevin Hickey]

We use HIGHMEM on the Au1300 to access any memory spaces >256 MB.  Our
I/O area starts at 256 MB.  We just map the extra DRAM to any area
outside the I/O space, enable highmem, and register it as BOOT_MEM_RAM
with add_memory_region.  Works great.

=Kevin
--
Kevin Hickey
Netlogic Microsystems


On Wed, 2009-11-25 at 14:34 +0800, figo zhang wrote:
> hi all,
> 
> I am using 24KEC SOC, i want to support larger more than 512MB RAM.
> The mips32 architure  in Kseg0/Kseg1,
> such as:
> 0x8000,0000 ~ 0x92c0,0000  # 300MB for RAM
> 0x92c0,0000 ~ 0xa000,0000  # 212 for I/O register
> 
> so, mips32 only support 300MB memory, i dont how to support more than
> 512MB in linux-mips kernel , such as 2GB memory? it is using HIGHMEM
> strategy
> for kernel(ZONE_HIGHMEM)?
> 
> Best,
> Figo.zhang

Re: how to support more than 512MB RAM for MIPS32 ?

[Figo.zhang]

On Wed, 2009-11-25 at 08:37 -0600, Kevin Hickey wrote:
> We use HIGHMEM on the Au1300 to access any memory spaces >256 MB.  Our
> I/O area starts at 256 MB.  We just map the extra DRAM to any area
> outside the I/O space,

how to do map extra RAM to any ouside I/O space?
it is just motify:

1. arch/mips/kernel/setup.c: bootm_init()function, motity the define
"HIGHMEM_START", for me: 
#define HIGHMEM_START 0x2000,0000   //512MB

2. use add_memory_region, for me:
 add_memory_region(0x20000000, 0x40000000, BOOT_MEM_RAM); //extra 1G RAM

is it ok ?

Best,
Figo.zhang


>  enable highmem, and register it as BOOT_MEM_RAM
> with add_memory_region.  Works great.
> 
> =Kevin
> --
> Kevin Hickey
> Netlogic Microsystems
> 
> 
> On Wed, 2009-11-25 at 14:34 +0800, figo zhang wrote:
> > hi all,
> > 
> > I am using 24KEC SOC, i want to support larger more than 512MB RAM.
> > The mips32 architure  in Kseg0/Kseg1,
> > such as:
> > 0x8000,0000 ~ 0x92c0,0000  # 300MB for RAM
> > 0x92c0,0000 ~ 0xa000,0000  # 212 for I/O register
> > 
> > so, mips32 only support 300MB memory, i dont how to support more than
> > 512MB in linux-mips kernel , such as 2GB memory? it is using HIGHMEM
> > strategy
> > for kernel(ZONE_HIGHMEM)?
> > 
> > Best,
> > Figo.zhang
> 

Re: how to support more than 512MB RAM for MIPS32 ?

[Ralf Baechle]

On Wed, Nov 25, 2009 at 11:31:14PM +0800, Figo.zhang wrote:

> how to do map extra RAM to any ouside I/O space?
> it is just motify:
> 
> 1. arch/mips/kernel/setup.c: bootm_init()function, motity the define
> "HIGHMEM_START", for me: 
> #define HIGHMEM_START 0x2000,0000   //512MB

Leave HIGHMEM_START unchanged; it should always be 512MB no matter what
the actual memory addresses of a particular platform are.  The kernel
needs to treat anything above 512MB differently because it's not
permanently mapped and HIGHMEM_START stands for this limit.

  Ralf

Re: how to support more than 512MB RAM for MIPS32 ?

[Figo.zhang]

On Wed, 2009-11-25 at 16:00 +0000, Ralf Baechle wrote:
> On Wed, Nov 25, 2009 at 11:31:14PM +0800, Figo.zhang wrote:
> 
> > how to do map extra RAM to any ouside I/O space?
> > it is just motify:
> > 
> > 1. arch/mips/kernel/setup.c: bootm_init()function, motity the define
> > "HIGHMEM_START", for me: 
> > #define HIGHMEM_START 0x2000,0000   //512MB
> 
> Leave HIGHMEM_START unchanged; it should always be 512MB no matter what
> the actual memory addresses of a particular platform are.  The kernel
> needs to treat anything above 512MB differently because it's not
> permanently mapped and HIGHMEM_START stands for this limit.
> 

HIGHMEM canot directly invoke __get_free_pages() to allocate pages, so
it would slow performance ?

Is it anyother solution in current linux-mips kernel? for example,
directly map extra RAM to 0x40000000~0x80000000, the user space
decreased, only 0x0~0x40000000.

Best,
Figo.zhang

>   Ralf