device tree in open firmware on power6

device tree in open firmware on power6

[Chandru]

Hi,

When I set linux 2.6.26-rc1 as default kernel to boot in 
/etc/yaboot.conf, then the device tree in open firmware shows only one 
memory node ( the same memory node appears in /proc/device-tree/memory@0 
).  But when RHEL5.2 kernel is set as default in /etc/yaboot.conf then 
the device tree in open firmware shows plenty of memory nodes. Following 
is the open firmware output..

linux-2.6.26-rc1:

<snip>
0 > dev / ls
...
000000caf1b8:   /PowerPC,POWER6@6
000000cb0120: /memory@0
000000cb83d8: /ibm,dynamic-reconfiguration-memory
000000cbcd60: /options
...

0 > dev /memory@0  ok
0 > .properties
name                    memory
device_type             memory
reg                     00000000 00000000  00000000 08000000
available               00000000 00004000 00000000 00bfc000 00000000 02020000
00000000 05fe0000
#address-cells          00000001
#size-cells             00000000
ibm,phandle             fffffffa
ibm,associativity       00000004 00000000 00000000 00000000 00000000

<snip-end>




when default=RHEL5.2:

0 > dev / ls 
000000c8d200: /ibm,serial
000000c8dff8: /chosen
...
000000cae2c0:   /PowerPC,POWER6@4
000000caf1b8:   /PowerPC,POWER6@6
000000cb0120: /memory@0
000000cb5af0: /memory@8000000
000000cb5ce0: /memory@c000000
000000cb5ed0: /memory@10000000
000000cb60c0: /memory@14000000
000000cb62b0: /memory@18000000
000000cb64a0: /memory@1c000000
000000cb6690: /memory@20000000

...


The open firmware environment variable "ibm,fw-new-mem-def" is false for 
rhel5.2 kernel where as it is 'true' for 2.6.26-rc1 as default kernel to 
boot.  Any inputs if the one memory node in 2.6.26-rc1 should show the 
size of available system memory ?, or there should be many memory nodes 
for 2.6.26-rc1 ?.

Thanks,
Chandru

Re: device tree in open firmware on power6

[Paul Mackerras]

Chandru writes:

> When I set linux 2.6.26-rc1 as default kernel to boot in 
> /etc/yaboot.conf, then the device tree in open firmware shows only one 
> memory node ( the same memory node appears in /proc/device-tree/memory@0 
> ).  But when RHEL5.2 kernel is set as default in /etc/yaboot.conf then 
> the device tree in open firmware shows plenty of memory nodes. Following 
> is the open firmware output..

Current kernels tell the firmware that they can handle having memory
represented in the /ibm,dynamic-reconfiguration-memory node, which is
a more compact representation than having it represented in multiple
/memory@xxx nodes.  Therefore firmware reports most of the memory in
the /ibm,dynamic-reconfiguration-memory node you have here:

> linux-2.6.26-rc1:
> 
> <snip>
> 0 > dev / ls
> ...
> 000000caf1b8:   /PowerPC,POWER6@6
> 000000cb0120: /memory@0
> 000000cb83d8: /ibm,dynamic-reconfiguration-memory

and only gives you one /memory@xxx node, which represents the real
memory area.  See sections C.6.2.3 and C.6.6.2 of PAPR for more
information.

Paul.