linux boot sequence

Siva Prasad sprasad at
Fri Jul 18 06:21:24 EST 2008


I am copy pasting a portion of my dts file. Here I am mentioning 2GB of memory. However, U-Boot can update this automatically, as u-boot is OF aware.

        memory {
                device_type = "memory";
                reg = <00000000 80000000>;

What is the boot loader you are using?

With the latest kernels you should be on arch/powerpc, not arch/ppc. I am not sure about the support for your PPC405 in powerpc.

- Siva

-----Original Message-----
From: Rami WEHBI [mailto:rwehbi at] 
Sent: Thursday, July 17, 2008 5:42 AM
To: Siva Prasad
Cc: linuxppc-embedded at
Subject: RE: linux boot sequence

Hello Siva,

I am using the 2.6.23 kernel and the target is the ppc405. 

Using the booting-without-of.txt, and in searching in the kernel code I found that the devices_info are passed as parameters (memory size is the parameter I am searching for) by calling the function "find_bootinfo(void)" in /arch/ppc/kernel/setup.c
This function initializes send the pointer to linux on the device info as following (line 345):

		Rec = (struct bi_record *) _ALIGN((ulong)__bss_start+(1<<20)-1,(1<<20));

What is this address stand for ??? 


-----Message d'origine-----
De : at [ at] De la part de Siva Prasad
Envoyé : mercredi 16 juillet 2008 20:46
À : Rami WEHBI
Cc : linuxppc-embedded at
Objet : RE: linux boot sequence


Please make sure to copy the list as well.

OF - Open firmware. I am not sure which version of Linux kernel you are using, and which boot loader. Lately it is all OF based, however it is supported in the form of device tree blob/structure. For more information read booting-without-of.txt in Documentation/powerpc.

U-Boot updates the detected memory in the dtb you loaded, so that when kernel reads it, correct information is provided.

There is no auto-detect option in kernel. You need to write your own code at the exact location it needs to identify the size of memory. Typically this is passed to the kernel either through DTB or kernel arguments.

Good Luck.

- Siva

-----Original Message-----
From: Rami WEHBI [mailto:rwehbi at]
Sent: Monday, July 14, 2008 11:47 PM
To: Siva Prasad
Subject: RE: linux boot sequence

 what is the OF dtb ??? And how does the bootloader update it ???

 How can I do to set the autodetect option in the kernel ???

Best Regards,

-----Message d'origine-----
De : Siva Prasad [mailto:sprasad at] 
Envoyé : vendredi 11 juillet 2008 23:01
À : Rami WEHBI
Cc : linuxppc-embedded at
Objet : linux boot sequence

Well!... You can pass the size as part of the OF memory=<>.

Typically your boot loader should detect the amount of memory on the system and update the OF dtb to reflect the available memory.

You may also tweak the kernel yourself to autodetect, instead of reading from the OF. How ever, I would recommend the previous approach.

- Siva

Date: Fri, 11 Jul 2008 08:34:54 +0200
From: "Rami WEHBI" <rwehbi at>
Subject: linux boot sequence
To: <linuxppc-embedded at>
<D3C541E264C021479BFB60B3B790C0FB497014 at etoilenoire.STARWARS.local>
Content-Type: text/plain; charset="iso-8859-1"

Hi all,
    I am using the ppc405 and I would like to know, how does linux on this architect detect the available memory size in details !!!
        is it a parameter passed to linux at startup by the boot loader ??
        is it an automatic detection ?? what are the steps to accomplish this job then ???
Best regards to all,

Rami WEHBI 	
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T?l :	 +33 2 36 56 86 00	
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