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Bug#667681: flash-kernel: Please add support for Dreamplug / Marvell Kirkwood FDT

On Thu, 2012-04-05 at 14:11 -0700, Martin Michlmayr wrote:
> * Ian Campbell <ijc@hellion.org.uk> [2012-04-05 20:24]:
> > Support has been added ot the uypstream kernel for the Dreamplug as a FDT
> > machine type. Accordingly the attached patch adds the necessary db enry for
> > this class of machines. Please consider applying.
> I'm not the maintainer of flash-kernel anymore and haven't followed DT
> in detail so maybe this question is stupid... but: where does the DT
> blob come from?  Shouldn't flash-kernel embed that into the kernel
> image, or do you require a DT compatible u-boot which will pass the DT
> to the kernel directly?

It requires a u-boot with FDT support, #667680 is my request to add that
patch to Debian u-boot.

There is an option to include a DTB in the kernel
(CONFIG_ARM_APPENDED_DTB) but the warnings in the Kconfig are a bit
scary and explicitly say it is for compatibility with non-DT capable

I'm working on a patch to include the actual blobs in the relevant
kernel image package.

> I guess you're using a DT compatible u-boot and I think on the
> DreamPlug it's fair enough to require users to upgrade to such a
> u-boot.

I think so, yes. u-boot as shipped with the dreamplug has a broken
machid so you pretty much have to reflash it anyway. The JTAG attachment
for the dreamplug is fairly cheap (~£30) and easily available (and the
software is in Debian) so reflashing is reasonably safe.

> (I have other devices in mind that don't ship with a DT u-boot and
> where you cannot easily upgrade u-boot; in those cases flash-kernel
> will have to embed the DT blob into the kernel image or something.)

For devices which currently use the old system nothing should change, a
single kernel image can support both FDT and machid things at the same
time. So for example the existing support for Sheevaplugs etc in the
kirkwood flavour are unchanged.

I guess upstream is forcing all new board ports to use DT, which will
certainly be a pain for boards with a non DT bootloader.

> Also, does it really say "Machine: Marvell Kirkwood (Flattened Device Tree)"?

Yes, it really does say that. I thought it was weird too but grepping
around in arch/arm it seems to be a fairly common structure (although
things aren't all that consistent)

> Is there no way to set the Machine info in /proc/cpuinfo to something
> more useful with the use of DT?

You mean to dynamically set it to something relevant to the actual
board? I don't see anything with a quick grep in the kernel. It
certainly seems like it would be a good thing for the kernel to do, I'll

> In any case, thanks or working on DreamPlug support!
> P.S. your git patch contains your company address but I guess this
> wasn't done on company time.

Oops yes, I used one of the faster ARM boards at work to do the build
and so I ended up committing it there too.

Ian Campbell

"With molasses you catch flies, with vinegar you catch nobody."
		-- Baltimore City Councilman Dominic DiPietro

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