Subject: Re: Reserving small amounts of memory with mem= (MPC85xx, 2.6.15 arch/ppc)

From: Florian Boelstler <[email-masked]>
Date: Fri, 13 Jun 2008 16:30:37 +0200

Hi,

thanks for your response.

Sylvain Joyeau wrote:
> Residual memory size is what Linux couldn't map with its three CAM
> entries. The main figure you can check is the sum of the three first
> CAMs   plus residual is what you specified (CAM0+CAM1+CAM2+residuak ==
> 'mem'). It's not weird to get a residual != 0 when specified memory
> size isn't a good combination of power of 2.

Again I tried mem=508M together with initrd_high @ 10000000. This time 
the kernel booted.
Shown mapping is: CAM0=256Mb, CAM1=64Mb, CAM2=64Mb residual: 124Mb, 
which is == 'mem'.

Available system memory is only 384 MB (CAM0+CAM1+CAM2), which explains 
why Linux "removed" the ramdisk, when it has been copied right below 
508M by U-Boot. Because at that time I was using initrd_high @ 1FC00000, 
which is outside of mapped RAM.

Is there an option to map less than 64M by a CAM entry?

> Stupid question: have you tried mem=512M and a correct RAM disk address ?
> No more comments...

I just did that (I don't get what you wanted to achieve with these 
settings, since this the default):

=> setenv bootargs console=ttyS0,115200 mem=512M
=> setenv initrd_high 20000000
=> bootm 0x02100000

## Booting image at 02100000 ...
    Image Name:   Linux 2.6.15
    Image Type:   PowerPC Linux Multi-File Image (gzip compressed)
    Data Size:    6965022 Bytes =  6.6 MB
    Load Address: 00000000
    Entry Point:  00000000
    Contents:
    Image 0:  1099550 Bytes =  1 MB
    Image 1:  5865458 Bytes =  5.6 MB
    Verifying Checksum ... OK
    Uncompressing Multi-File Image ... OK
## Current stack ends at 0x1FFAECB8 => set upper limit to 0x00800000
[...]

## initrd at 0x0220C76C ... 0x027A475D (len=5865458=0x597FF2)
    Loading Ramdisk to 1fa16000, end 1ffadff2 ... OK
## Transferring control to Linux (at address 00000000) ...
Memory CAM mapping: CAM0=256Mb, CAM1=256Mb, CAM2=0Mb residual: 0Mb
Linux version 2.6.15 (flo@escape) (gcc version 3.4.3) #21 PREEMPT Fri 
Nov 30 16:47:32 CET 2007
[...]

Have a nice weekend,

   Florian