[PATCH v7 14/31] arm: highbank: Add devicetree files

Simon Glass sjg at chromium.org
Tue Dec 7 16:07:17 CET 2021

Hi Andre,

On Mon, 6 Dec 2021 at 18:01, Andre Przywara <andre.przywara at arm.com> wrote:
> On Mon,  6 Dec 2021 17:11:52 -0700
> Simon Glass <sjg at chromium.org> wrote:
> > Sync these files, obtained from Linux v5.15.
> Sorry, but this would be wrong.
> How do you know which board it is? Highbank or Midway? We use the
> same binary for both, and decide either by the DT nodes we find in DRAM
> or by some autodetection (Cortex-A9 vs. Cortex-A15) if there are
> differences. The memory size would possibly be wrong (it's a DIMM slot).
> If you need *some* DT for build reasons, whatever, but at least go with
> the empty stub.
> And I still don't get this whole development argument: Why would
> anyone need some random or partial DT sample in the U-Boot tree to do
> development?
> If people develop a driver, the document to code against is the
> *binding* documentation, which describes what to expect from the DT
> nodes. Then you *test* it against an actual tree, but on the actual
> hardware, in which case you get the actual DTB, from the board.
> If a developer needs to take a sneak peek into an actual DTB,
> there are so many simple ways to do that: QEMU's dumpdtb, RPi's SD
> card content, U-Boot's "fdt addr $fdtcontroladdr; fdt print", the
> kernel's /sys/firmware/devicetree/base, ... When you port U-Boot to a
> board, getting hands on the actual DT is probably the least of your
> problems.
> So why would we need some mostly wrong DTs in the U-Boot tree?
> It seems to suggest that you can hack the DT to make things work, but
> this sounds bonkers, as the real DTB comes from somewhere else (SPI
> flash, SD card, generated based on command line), and patching U-Boot's
> copy to make things work is just wishful thinking.
> I can see the hacker's desire to play around with the DTB from time
> to time (What happens if the GPIO is wrong? Can we deal with two
> instances of the same device?), but for those experiments there are
> plenty of ways to achieve this - and be it temporarily replacing the
> empty DT stub. I just feel that bending the (board's) DT design ideas
> for a hacker's pleasure is not justified.

What, there are two boards? How was I supposed to know that?

Where do the devicetree files come from? I was assuming it was Linux,
but are they not even there? It doesn't really matter what the tree
is, but I assume the base tree must come from *somewhere*. We want to
sync that to U-Boot.

Please add a doc/board/highbank.rts or similar.

I think you have missed a lot of discussion about all this.


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