[PATCH v2] ARM: tegra: add Acer Chromebook 13 device tree

[Andrew Bresticker]

> It's been a long time since I've used FIT, but I seem to remember that
> it was simply a device tree-based description of a file format. As such
> couldn't you add an additional property to the configuration entry that
> the bootloader could match on? That would avoid the need to parse an
> embedded device tree and it might be useful to keep variants for the
> same board in the same FIT image.

Yes, I suppose something like that would be possible, however it's not
just depthcharge that matches to configurations based on the
compatible string within the configuration's FDT blob, this is the
convention U-Boot uses as well when booting FIT images.

> Perhaps you can explain a little more what the use-cases are. For
> example how are people suppose to run an upstream kernel on one of these
> Chromebooks?

There are a few ways you could run an upstream kernel:

1) Building your own verified-boot-wrapped FIT image and replacing the
existing one using tools found in the ChromiumOS tree [0].  This is
the workflow must of our developers use when working on product
kernels, but could just as easily be done with an upstream kernel.

2) Using U-Boot, either through the built-in legacy mode payload
(Ctrl-L at the developer screen) or by replacing the vboot-wrapped FIT
image with one that has U-Boot as a payload rather than a kernel [1].

3) If you're willing to flash your own firmware to the device, you can
build netboot-enabled firmware form the ChromiumOS tree that will load
a FIT image over the network.  This is the most flexible, as it
doesn't require the root device to be partitioned in any particular
way and allows you to boot non-ChromeOS distributions (e.g. Ubuntu).
This is what Dylan and I usually do when working on upstream kernels.

> How does dual-booting work?

You could dual-boot with the legacy-mode U-Boot, described above.

> Does the user get a menu to choose a configuration they want to boot if
> multiple entries are compatible with the detected board?

IIRC depthcharge will just pick the first one if there are multiple
exact matches.

[0] http://www.chromium.org/chromium-os/how-tos-and-troubleshooting/kernel-faq#TOC-How-to-quickly-test-kernel-modifications-the-fast-way-
[1] http://www.chromium.org/chromium-os/u-boot-porting-guide/using-nv-u-boot-on-the-samsung-arm-chromebook#TOC-Installing-nv-U-Boot-chained-U-Boot-method-