Re: Guix on the ASUS C201PA

[Vagrant Cascadian]

On 2019-03-06, Timothy Sample wrote:
> I was able to get Guix to boot on an ASUS Chromebook C201PA.  This model
> of computer is pretty neat.  It’s an ARMv7 (32-bit) machine that can be
> run with entirely free software.  There is even a free graphics driver
> in the works [1].

Very excited to try this!

I've been working on getting Debian to work on it for years, and had it
working with linux 4.8.x... and then haven't gotten it working with any
kernel version since. I've very recently been trying to get Archlinux
and Parabola working on it, but haven't gotten very far yet...


> For the bootloader, these machines use Depthcharge.  Depthcharge boots a
> specially packaged and signed kernel image from a specially marked
> partition.  This kernel image is written to the partition directly
> without a file system.

I have two big technical frustrations with Depthcharge:

It's really hard to debug or select alternate kernels when boot is
failing.

The kernel+initrd is limited to ~16MB. linux-libre on armhf is about
5MB, and the initrd around 11MB... so it's running pretty close to that
limit (Debian initrd's are even larger these days). I even increased the
size of the partition to 32MB to see if it would work, but it refused to
boot from anything larger than 16MB.


> There may be a way to improve this by bringing U-Boot into the booting
> process.  The next version of U-Boot (to be released in April) will
> support this machine directly.

My recent renewed interest is actually to test the chromebook_speedy
u-boot target included upstream... but the LCD doesn't work with my
particular C201PA, and there's no simple to access serial console, so
apparently not all variants are supported yet; am working with the
person who added support to u-boot to get that fixed, though.


> Alternatively, if using U-Boot directly causes problems, it’s possible
> that Depthcharge could boot into U-Boot.

That would be interesting to get working, though I'm not sure that's
supported in the current chromebook_speedy target in u-boot. Would be
easier to test (u-boot should fit in 16MB just fine for the forseeable
future!).

Thanks for working on it, and I'll try it out and report back.


live well,
  vagrant

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