DTS for PowerPC 440 based board

DTS for PowerPC 440 based board

[Vinayak Kale]

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

Thanks
Vinayak

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Re: DTS for PowerPC 440 based board

[David Gibson]

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_!
http://www.ozlabs.org/~dgibson

Re: DTS for PowerPC 440 based board

[Grant Likely]

On Sat, Nov 21, 2009 at 2:20 PM, David Gibson
<david@gibson.dropbear.id.au> wrote:
> On Sun, Nov 22, 2009 at 12:16:59AM +0530, Vinayak Kale wrote:
>> 2) If uboot passes BDInfo struct to kernel instead of DT blob, then in t=
his
>> case does kernel creates FDT at run time?
>
> Not exactly. =A0In this case the bootwrapper will be built with an FDT
> (compiled from a dts) built in. =A0It will however tweak the FDT with
> information from the BDInfo before booting the kernel proper.

...but if you have any sort of choice, save yourself some trouble and
enable FDT support in u-boot.  Then you don't need to muck about with
problematic bd_info structures.

g.

--=20
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.