[U-Boot] Help on U-Boot and Linux integration on PPC cpus

[Jerry Van Baren]

Luigi 'Comio' Mantellini wrote:
> Hi Ml,
> 
> I'm working on a ppc8541 based board. I ported the U-boot board just creationg 
> a "strip-down" version of frescale8541 board (I don't use TSEC and Quicc, 
> ...)-
> My next task is to have the first boot with linux and I'm a lot confused by fdt 
> usage.
> 
> In the past I always worked on mips based SoC and the ppc is a new world for 
> me, then my apologies for my stupid questions.

s/ppc/powerpc/ - the linux ppc arch doesn't support fdt. ;-)

> I have a couple of (trivial) question/doubts  regarding the fdt usage:
> 
> 1) I created my dts/dtb (exentially copying a 8541 board): How can this object 
> be used by u-boot? should I copy it into the flash (for example)?

Strictly speaking, it isn't *used* by u-boot, but it is manipulated by 
u-boot to fix it up / augment it to describe the board's hardware.  It 
is then *used* by linux - it allows one linux image to boot on a wide 
variety of boards (MAJOR win).

You need to pass a fdt blob to the linux kernel.  As always, there are 
many ways to do this.  One way is to program it into flash.  This is 
great if your blob is stable (e.g. good for manufacturing).  Another way 
is to tftp the blob over from your server along with your linux image.

The *slickest* way by far is to use a FIT image - this wraps 
*everything* (kernel, board fdt blob, ramdisk) in a fdt blob.  See
   u-boot/doc/uimage.FIT

<http://git.denx.de/?p=u-boot.git;a=tree;f=doc/uImage.FIT;h=f1d03d7350a164ee6c951ea239a0e0e72db0e81b;hb=HEAD>

> 2) is there a how-to or a survey regarding the fdt usage into u-boot (and 
> linux kernel)?

There are various fdt whitepapers out there and *how* the fdt is used by 
linux is documented in the linux source tree.  For PowerPC processors:
   linux/Documentation/powerpc

<http://git.denx.de/?p=linux-2.6-denx.git;a=tree;f=Documentation/powerpc;h=01939ab891de2b352c4e9185d1f6bc667436bfb3;hb=HEAD>

> thanks for help,
> 
> luigi

Best regards,
gvb