Re: DTS for PowerPC 440 based board

[David Gibson <david@gibson.dropbear.id.au>]

On Sun, Nov 22, 2009 at 12:16:59AM +0530, Vinayak Kale wrote:
> Hi,
> I am porting 2.6.31 for a PowerPC 440 core based board. I have couple of
> queries. I would really appreciate if someone could answer since i couldn't
> find info from other places.
> 
> 1) Is it mandatory to create a DTS file?

Roughly speaking, yes.  You have to supply a device tree to the
kernel somehow, so if the firmware doesn't supply one itself, you will
need to create a DTS.

> 2) If uboot passes BDInfo struct to kernel instead of DT blob, then in this
> case does kernel creates FDT at run time?

Not exactly.  In this case the bootwrapper will be built with an FDT
(compiled from a dts) built in.  It will however tweak the FDT with
information from the BDInfo before booting the kernel proper.

> 3) I believe in case of DTS, the kernel picks up the h/w info from DTS blob
> so we need not hardcode any register addresses etc inside kernel other than
> in dts file. What happens in case of uboot passing just BDInfo struct. How
> do we specify the register addresses etc?

There's always a device tree which specifies register addresses.  If
the firmware only supplies a BDInfo, then the kernel wrapper must have
a device tree built in.  In practice that will always be built from a
dts, though it doesn't have to be in theory.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
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