Re: [Xen-devel] [PATCH RFC OSSTEST 14/19] Osstest/Debian: Support for loading an FDT from u-boot script

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Fri, 2014-10-10 at 15:29 +0100, Ian Jackson wrote:
> I confess I don't really understand some of this.  `Platforms which do
> not provide an fdt' are ones where ${fdt_addr} is empty ?

Yes.

Midway (marilith) provides a dtb in the firmware, and it is located at
$fdt_addr. This is how device tree is supposed to work, but is actually
vanishingly rare on ARM+u-boot in real life (I've never seen another
such platform...)

In practice most ARM+u-boot platforms require you to load the dtb from
somewhere by hand, and provide fdt_addr_r as the place you should put
it.

(EFI on arm64 is a bit better here...)

>   And on
> those platforms `fdt addr \${fdt_addr}' is a no-op ?

fdt_addr is set by the new code on those platforms.

> You might find the code clearer (less toothpick-counting) if you used
> <<'delim' for some of it, at one or other of the levels.

You mean as opposed to <<delim because it changes the quoting behaviour?

That would break places where I wanted to expand a Perl var, I think?
Perhaps those uses can be broken out in some convenient way and
concatenated back again. I'll give it a go and see how it looks.

Ian.


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