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Re: booting the samsung chromeboot xe303c12 with the debian armmp kernel



On Mon, Nov 17 2014, Ian Campbell wrote:
>> Having built a kernel[1] with CONFIG_FB_SIMPLE and adding the
>> flash-kernel support, I can properly generate the kernel, initrd and dtb
>> images, but the result still doesn't usefully boot.
>> 
>> When I run 'bootm ...' there is some text printed by the loader (much as
>> before CONFIG_FB_SIMPLE), and then the screen clears to blank.
>
> I don't know a whole lot about this fb simple stuff, but doesn't it
> require the bootloader to pass in some DT nodes telling it where it
> ended up putting things?

Yes, I believe so.

> Does the u-boot you have do that?

There are two nv-uboot binaries available for this Chromebook - one is
supposed to have simplefb support. Looking at the binary I have, it does
include the string "simple-framebuffer". Rebuilding the binary is
documented[1], but involves jumping on board the Chrome OS build train,
as best I can figure.

> The protocol was only recently agreed (although there was some sort of
> precursor in the field).
>
> Sorry to be so fluffy, I only have the vaguest notion of how any of this
> stuff fits together...

Presumably it's obvious that I know less :-)

There is a comment[2] on linux-exynos.org which says that the mainline
kernel doesn't have the relevant DTS updates, so perhaps they are also
missing from the Debian kernel tree.

Looking at the linux-exynos tree referenced, I can't see any
"simple-framebuffer" nodes in the .dts files themselves. Is u-boot
expected to add nodes to the tree before providing it to the kernel?

>> [1]  Which took many hours on a Banana Pi...
>
> I bet it did!
>
> FWIW I often build on x86 with the aarch64-linux-gnu-gcc cross compiler
> from Linaro in my $PATH and
>  dpkg-buildpackage -aarmhf -<other usual options>
>
> IIRC I had to add a symlink because Linaro's compiler includes more/less
> elements of the version number compared to what the kernel build system
> expects (i.e. ...-gcc-4.8 vs ...-gcc-4.8.3 etc, I don't recall which way
> round it was though...)

It's okay for the Pi to take ages - I can get on with real work while it
is building.

Footnotes: 
[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-
[2]  http://linux-exynos.org/wiki/ARM_Chromebook/Mainline_Linux_kernel


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