Adding support for Orange Pi Zero 3

[Bob McChesney]

On Thu, Nov 23, 2023 at 03:17:09PM +0000, Andre Przywara wrote:
> On Sat, 4 Nov 2023 19:17:44 +0000
> electricworry <worryelectric at gmail.com> wrote:
> 
> Hi,
> 
> > I would like to contribute improvements u-boot to enable support for
> > the Orange Pi Zero 3 board. I have already gained a good understanding
> > of the project and the standards for changes, and so I have made
> > modifications and tested them on my board.
> 
> thanks for your interest and for reaching out!
> 
> I will answer your questions below, but for this particular topic there
> are already support patches on the list (sorry for the disappointment!):
> https://lore.kernel.org/u-boot/20231114013106.31336-1-andre.przywara@arm.com/

That's good. I'm happy that more experienced people have been working on
this. It's been a good learning experience nevertheless.

> Can you please apply those patches on top of mainline U-Boot and test
> them? Then reply to patch 3/3 above with a Tested-by: line, stating your
> name and email address?
> Having independent reports of that working would make me more confident in
> merging the series.

I'm happy to do that and will be able to do it shortly. In this case
would I be applying the patches on top of the next branch?

> As a general advice: try to reach out early, to avoid working in parallel
> on something, and also to avoid working in the wrong direction.
> There is the #linux-sunxi IRC channel on the OFTC IRC network[1] (you can
> join via any browser), also there is a mailing list for Allwinner related
> upstream work: linux-sunxi at lists.linux.dev [2]
> Another resource is our wiki: https://linux-sunxi.org
> 
> [1] https://www.oftc.net/WebChat/
>     https://oftc.irclog.whitequark.org/linux-sunxi
> [2] https://subspace.kernel.org/lists.linux.dev.html

Thank you. I wasn't aware of this community and have been working alone.
It will be more productive to work and discuss with others so I'll join
that mailing list too.

> > Before submitting patches for review I've got a few questions I'd like
> > to discuss.
> > 
> > The board is an Allwinner H618. From what I can gather this is just an
> > H616 with minor changes. The changes are so minor that I've been able
> > to implement the support as changes to the existing files for H616.
> 
> Just curious, what changes did you find in particular? So far we know
> about the increased L2 cache, which is irrelevant from a software support
> perspective, and the change of base address and layout of the CPUX_CFG
> block, which is already covered by:
> https://source.denx.de/u-boot/u-boot/-/commit/0a137ac5015933bf38ea2700abe70602ef63bbdd
> Did you find anything else?

I am not what anyone could call a hardware expert so I've just been
working by diffing the codebase from the vendor against u-boot mainline.
Changes that I've created patches for include their full dtb, the LPDDR4
support, the AXP313A power, and - perhaps incorrectly - zeroing a
register so that the thermal driver in the kernel works properly and
doesn't get false high temperature readings. I say "perhaps incorrectly"
because I feel like the kernel driver should be doing that work itself
and the comment in the vendor u-boot code suggests it's a hack: "The
bit[16] of register reg[0x03000000] must be zero for the THS driver to
work properly in the kernel. The BSP u-boot is putting the whole
register to zero so we are doing the same."

> Out of interest, how did you do this? Disassembled the vendor boot0?
> Dumping DRAM registers? We discussed and tested the LPDDR4 support already
> a while ago, and support for that was merged recently:
> https://source.denx.de/u-boot/u-boot/-/commit/4b02f0120a4bb2a5d7081aef8cef6a4ca57e9db2

As above, I didn't do anything clever like probe hardware or
disassemble binaries; it was just a brute force loop of cherry-picking,
compiling and testing. And also doing it in a way that fitted the
incumbent style and practices of mainline. e.g. making use of configs
like CONFIG_DRAM_SUN50I_H616_DX_ODT for the board family rathern than
having board specific ifdefs. The work done is available if anyone wants
to see it, and I'd be happy to have it critiqued. Looking at the patches
proposed here I'm happy to see that we've come to the same conclusion on
some things (such as the above config) and others we diverge on, but as
I can see from the discussion in linux-sunxi the feeling is that some of
these difference don't matter.

> Hope that helps!
> 
> Cheers,
> Andre

Thanks for all of that good advice. It's immensely appreciated. I'll
keep this as a guide for contibuting patches in the future.

Now that there's a working u-boot for the board - I've got two to choose
from now :) - I'm going to be concentrating on trying to get the Mali
graphics working as it's a requirement for my project. I've got a
working kernel (6.1.31 with patches) but I can also see that work's been
underway to bring the support to 6.7. I tested 6.7-rc2 today and can't
get any output at all on the console after u-boot starts the kernel.

Cheers,
Bob