[Dev] Looking for help to officially support the lime2 (and the lime2-emmc)

[Denis 'GNUtoo' Carikli]

Hi,

Parabola has currently some incomplete support for the Lime2.

When we go on Olimex website on the page of the lime2 on their shop, we
can see several versions[1]:
- A20-OLinuXino-LIME2
- A20-OLinuXino-LIME2-e16Gs16M
- A20-OLinuXIno-LIME2-n8G
- A20-OLinuXino-LIME2-s16M
- T2-OLinuXino-LIME2-e8Gs16M-IND
- T2-OLinuXino-LIME2-IND
- T2-OLinuXino-LIME2-s16M-IND

And we can see in the description the differences between these
versions. For instance:
> 4GB or 16GB eMMC flash memory option (in A20-OLinuXino-LIME2-e4GB or
> A20-OLinuXino-LIME2-e16GB)

And from all that information, the Parabola contributors can deduce
which versions are supported or not and reference that on the Parabola
wiki on the device page[2] and the installation instructions[3]. 

Users then hopefully find out what version they have (for instance by
asking around or asking Olimex, or the people they got their lime2
from) and it could work if that was the only thing to take into account
(more details later).

The version of the Lime2 is important here because if you have the
standard lime 2 (A20-OLinuXino-LIME2) you need to install the
uboot4extlinux-a20-olinuxino-lime2 bootloader as part of the Parabola
installation instructions.

And if you instead have the versions with an eMMC
(A20-OLinuXino-LIME2-e4GB and A20-OLinuXino-LIME2-e16GB), you need to
install the uboot4extlinux-a20-olinuxino-lime2-emmc package instead.

The issue is that there are also less well known changes. On both the
standard lime2 and on the eMMC version, the Ethernet chip changed twice
(probably because the older ones weren't available anymore and because
the lime2 continues to be manufactured).

So I asked Olimex for 3 boards, one with each Ethernet chip, in order
to try to support all 3 Ethernet chips in upstream u-boot and/or Linux
with the same configuration.

Currently, there are (not upstream) u-boot configurations that are
tailored to specific Ethernet chips, but if we don't support all 3
Ethernet with the same configuration, users will need to know which
Ethernet chip they have, and most users won't know how to do that.
And with non-working Ethernet it's also harder to install the right
u-boot package when you picked the wrong one.

And if the support isn't upstream, we'd end up having to patch all the
FSDG compliant distributions out there, and possibly even the
upstream non-FSDG compliant distributions. So it looks way less work to
fix it upstream once for good and for everybody, and don't multiply the
build configurations and u-boot packages.

We have a bug report about that issue in Parabola[4]. 

The advantage of fixing that bug (instead of stopping the support
for the lime2 or not fixing it at all) is also that everything works
with free software on the Lime2, and that device keeps being produced
and sold for a lot of years and will most probably continue being
produced and sold. 

The only nonfree software required are the builtin firmwares that are
found in mass storage devices like hard disks, SSDs, microSD, etc.

Even things like the GPU and video decoding acceleration works with
free software here.

So to help us fix that, Olimex shipped the 3 Lime2 boards to
Sagar Acharya as not only I was already heavily involved in way too
many other projects, but it also gave the opportunity to Sagar to be
involved in fixing that bug upstream.

However new bugs appeared[5], and in some cases compiling and
booting Linux even resulted in crashes (we were unlucky), so learning
ARM specifics in these conditions is not ideal. 

I tried to help but I don't have time anymore for that as I'm extremely
late with Replicant (I am supposed to have released Replicant 11 and
6.0 0004 years ago, and there is still a lot to do for Replicant 11).

So a solution that could work would be (for the people interested) to
make bootloader and/or kernel packages to be easily installed in order
to test if the Ethernet works and start from there.

Since linux-libre releases recent kernels, including RC, we could add
patches on top if we need to. For u-boot we can also make a git package
if needed with patches on top.

One of the thing to take into account is also that we don't know if the
Ethernet hardware works on the lime2 with the first Ethernet chip that
we got. 

Olimex had to solder the only first Ethernet chip they got left on a
Lime2 specially for us as they didn't have lime2s anymore with this
version.

So we also need to find images that are known to work with this
Ethernet chip and it out to see if it's a hardware problem or a
software issue.

In the worst case we could fix it only for the two other Ethernet
chips, hoping that people don't have these boards anymore or that
they'd show up to help us with testing.

References:
-----------
[1]https://www.olimex.com/Products/OLinuXino/A20/A20-OLinuXino-LIME2/open-source-hardware
[2]https://wiki.parabola.nu/Computers/A20-OLinuXino-LIME2
[3]https://wiki.parabola.nu/ARM_Installation_Guide#Which_bootloader_package_to_use_for_which_device.3F
[4]https://labs.parabola.nu/issues/2945
[5]https://labs.parabola.nu/issues/3058

Denis.
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