[U-Boot-Users] Doubt regarding bootm in Uboot

[Grant Likely]

On 8/5/07, Yasothabalan Ramaswamy-TLS,Chennai <yasothabalanr at hcl.in> wrote:
> Hi all,
>
> I want to know how to transfer the control from Uboot to Linux Kernel. I am using MPC5200B powerpc and ICECUBE board.
>
> Where exactly the Linux Kernel should be loaded?

Wherever you want to load it.  u-boot will relocate it to the correct
location after uncompressing the kernel uImage file.

>
>
>
> In cmd_bootm.c file,
<snip>
> What do these lines signify?

There are 2 different directories in the Linux kernel source tree
which can be used to build a powerpc kernel; arch/ppc and
arch/powerpc.  arch/ppc is obsolete and slowly all board support in
arch/ppc is moving over to arch/powerpc (support for mpc5200 is
currently in both trees).

BTW, for new designs, you should be using arch/powerpc (by setting
ARCH=powerpc in the environment when building the kernel)

One significant difference between arch/ppc and arch/powerpc is how
the bootloader communicates with the kernel for embedded platforms.
In arch/ppc, u-boot passes data via a static structure which has no
standard format as is prone to breakage.  In arch/powerpc, the
bootloader instead passes a device tree blob which does have a
standard format, and is much less prone to breakage.

So, when booting your Linux kernel that was built with ARCH=powerpc,
you should pass three parameters to the bootm command.
1. address of the kernel
2. address of the (or '-' if you don't have one)
3. address of the device tree

You can generate a device tree blob (.dtb file) by compiling the dts
file for your board with the device tree compiler (dtc).  The
Lite5200B device tree is in the kernel source tree in the directory
arch/powerpc/boot/dts.

Side note: you're email client is sending mail in HTML, not plain
ASCII text.  Etiquette on this list is for ASCII email only.

Cheers,
g.



-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
grant.likely at secretlab.ca
(403) 399-0195