[PATCH v6 00/25] fdt: Make OF_BOARD a boolean option

[Simon Glass]

Hi Tom,

On Fri, 3 Dec 2021 at 13:43, Tom Rini <trini at konsulko.com> wrote:
>
> On Thu, Dec 02, 2021 at 07:03:30PM -0700, Simon Glass wrote:
> > Hi Andre,
> >
> > On Thu, 2 Dec 2021 at 18:59, Andre Przywara <andre.przywara at arm.com> wrote:
> > >
> > > On Thu, 2 Dec 2021 13:34:07 -0500
> > > Tom Rini <trini at konsulko.com> wrote:
> > >
> > > Hi,
> > >
> > > > On Thu, Dec 02, 2021 at 11:17:38AM -0700, Simon Glass wrote:
> > > > > Hi Tom,
> > > > >
> > > > > On Thu, 2 Dec 2021 at 11:03, Tom Rini <trini at konsulko.com> wrote:
> > > > > >
> > > > > > On Thu, Dec 02, 2021 at 10:07:13AM -0700, Simon Glass wrote:
> > > > > > > Hi Tom,
> > > > > > >
> > > > > > > On Thu, 2 Dec 2021 at 09:59, Tom Rini <trini at konsulko.com> wrote:
> > > > > > > >
> > > > > > > > On Thu, Dec 02, 2021 at 09:49:51AM -0700, Simon Glass wrote:
> > > > > > > > > Hi Tom,
> > > > > > > > >
> > > > > > > > > On Thu, 2 Dec 2021 at 09:38, Tom Rini <trini at konsulko.com> wrote:
> > > > > > > > > >
> > > > > > > > > > On Thu, Dec 02, 2021 at 05:33:53PM +0100, François Ozog wrote:
> > > > > > > > > > > Hi Simon
> > > > > > > > > > >
> > > > > > > > > > > Le jeu. 2 déc. 2021 à 17:00, Simon Glass <sjg at chromium.org> a écrit :
> > > > > > > > > > >
> > > > > > > > > > > > With Ilias' efforts we have dropped OF_PRIOR_STAGE and OF_HOSTFILE so
> > > > > > > > > > > > there are only three ways to obtain a devicetree:
> > > > > > > > > > > >
> > > > > > > > > > > >    - OF_SEPARATE - the normal way, where the devicetree is built and
> > > > > > > > > > > >       appended to U-Boot
> > > > > > > > > > > >    - OF_EMBED - for development purposes, the devicetree is embedded in
> > > > > > > > > > > >       the ELF file (also used for EFI)
> > > > > > > > > > > >    - OF_BOARD - the board figures it out on its own
> > > > > > > > > > > >
> > > > > > > > > > > > The last one is currently set up so that no devicetree is needed at all
> > > > > > > > > > > > in the U-Boot tree. Most boards do provide one, but some don't. Some
> > > > > > > > > > > > don't even provide instructions on how to boot on the board.
> > > > > > > > > > > >
> > > > > > > > > > > > The problems with this approach are documented in another patch in this
> > > > > > > > > > > > series: "doc: Add documentation about devicetree usage"
> > > > > > > > > > > >
> > > > > > > > > > > > In practice, OF_BOARD is not really distinct from OF_SEPARATE. Any board
> > > > > > > > > > > > can obtain its devicetree at runtime, even it is has a devicetree built
> > > > > > > > > > > > in U-Boot. This is because U-Boot may be a second-stage bootloader and its
> > > > > > > > > > > > caller may have a better idea about the hardware available in the machine.
> > > > > > > > > > > > This is the case with a few QEMU boards, for example.
> > > > > > > > > > > >
> > > > > > > > > > > > So it makes no sense to have OF_BOARD as a 'choice'. It should be an
> > > > > > > > > > > > option, available with either OF_SEPARATE or OF_EMBED.
> > > > > > > > > > > >
> > > > > > > > > > > > This series makes this change, adding various missing devicetree files
> > > > > > > > > > > > (and placeholders) to make the build work.
> > > > > > > > > > > >
> > > > > > > > > > > > Note: If board maintainers are able to add their own patch to add the
> > > > > > > > > > > > files, some patches in this series can be dropped.
> > > > > > > > > > > >
> > > > > > > > > > > > It also provides a few qemu clean-ups discovered along the way. The
> > > > > > > > > > > > qemu-riscv64_spl problem is fixed.
> > > > > > > > > > > >
> > > > > > > > > > > > [1]
> > > > > > > > > > > > https://patchwork.ozlabs.org/project/uboot/patch/20210919215111.3830278-3-sjg@chromium.org/
> > > > > > > > > > > >
> > > > > > > > > > > > Changes in v6:
> > > > > > > > > > > > - Fix description of OF_BOARD so it refers just to the current state
> > > > > > > > > > > > - Explain that the 'two devicetrees' refers to two *control* devicetrees
> > > > > > > > > > > > - Expand the commit message based on comments
> > > > > > > > > > > > - Expand the commit message based on comments
> > > > > > > > > > >
> > > > > > > > > > > You haven’t addressed any concerns expressed on the mailing list.so I am
> > > > > > > > > > > not in favor of this new version either.
> > > > > > > > > > > If you make a version without « fake DTs » as you name them, there are good
> > > > > > > > > > > advances in the documentation and other areas that would be better in
> > > > > > > > > > > mainline….
> > > > > > > > > > > If I am the only one thinking this way and the patch can be accepted, I
> > > > > > > > > > > would love there is a warning in capital letters at the top of the DTS fake
> > > > > > > > > > > files that explains the intent of this fake DT, the possible outcomes of
> > > > > > > > > > > not using the one provided by the platform and the right way of dealing
> > > > > > > > > > > with DTs for the platform.
> > > > > > > > > >
> > > > > > > > > > This is the part that I too am still unhappy about.  I do not want
> > > > > > > > > > reference or fake or whatever device trees in the U-Boot source tree.
> > > > > > > > > > We should be able to _remove_ the ones we have, that are not required,
> > > > > > > > > > with doc/board/...rst explaining how to get / view one.  Not adding
> > > > > > > > > > more.
> > > > > > > > >
> > > > > > > > > I understand you don't like it and that others don't as well. I wish
> > > > > > > > > it had not come to this.
> > > > > > > > >
> > > > > > > > > However we are only talking about 10 boards, three of which don't even
> > > > > > > > > have a devicetree anywhere I can find.
> > > > > > > > >
> > > > > > > > > I think on balance this is a substantial clean-up. I am happy to add
> > > > > > > > > whatever caveats and documentation people want to clarify what is
> > > > > > > > > going on here. I'm happy to look at future options where the
> > > > > > > > > devicetree is hosted elsewhere, so long as it is trivial to build it
> > > > > > > > > within U-Boot for development purposes.
> > > > > > > > >
> > > > > > > > > I'll also note that the bootstd series shows the devicetree source:
> > > > > > > > >
> > > > > > > > > Core:  246 devices, 88 uclasses, devicetree: board
> > > > > > > > >
> > > > > > > > > But for now, I still feel this is the best path forward.
> > > > > > > >
> > > > > > > > I'm not sure how to proceed here.  The reviews are rather strongly
> > > > > > > > against the "include a device tree that won't be used".  The use case of
> > > > > > > > "but for development someone might need to modify the device tree" is
> > > > > > > > handled by platforms documenting where / how to get the real one.  We
> > > > > > > > should even update the Kconfig help to note that if you enable this your
> > > > > > > > board docs MUST explain where the device tree can be seen (or have some
> > > > > > > > legal reason you think it's OK to not...).
> > > > > > >
> > > > > > > Right, we can do lots of things as we have discussed. I am very
> > > > > > > willing to work on these and make sure it is hard to do the thing. But
> > > > > > > this series is long enough already.
> > > > > >
> > > > > > Yes, I think the rest of us had hoped you would come around to all of
> > > > > > our reasoning by this point, is why this is taking so long.
> > > > > >
> > > > >
> > > > > Look, if I thought this was all wrong I would not be doing it. We have
> > > > > a range of opinions:
> > > >
> > > > And the rest of us wouldn't keep trying to argue otherwise if we didn't
> > > > see problems with it, still.
> > > >
> > > > > - U-Boot should not have its own nodes/properties
> > > >
> > > > The caveat there is that aren't documented upstream bindings.  I think
> > > > at this point the lack of screaming and otherwise "wait, no no no
> > > > don't!" that your current patch has gotten means it's time for a pull
> > > > request, and for that to go in, and so this line of argument would be
> > > > simply removed.
> > > >
> > > > > - U-Boot should not have DTs in-tree
> > > >
> > > > ... for the cases where the DTs are not used at run time, yes.
> > > >
> > > > > - U-Boot should have DTs only when essential
> > > >
> > > > I don't understand this point.  Can you please elaborate?
> > > >
> > > > > - U-Boot should have DTs in-tree for all boards
> > > >
> > > > This is the line you're pushing and almost every other reviewer
> > > > disagrees with.
> > > >
> > > > > What's the downside here anyway?
> > > >
> > > > - A lack of clarity.  We have dts files, you modify those dts files,
> > > >   they aren't used.  What's the point?  Oh, you forgot to tweak
> > > >   something else.  Wait, now nothing works.  Oh, it's a mismatch between
> > > >   what this dts was at one point, and what it needs to be now to
> > > >   actually work.
> > > > - We're adding more ongoing sync-up work.  While I loudly applaud the
> > > >   custodians that are keeping their dts files in sync very regularly,
> > > >   and I sympathize with the custodians that want to do it more, but are
> > > >   unable to find the time, I do not want to add more of this work.  Even
> > > >   more so when it's unclear who would be doing it.  Or what the use is.
> > > >
> > > > There's probably more if I think about it harder, but those are the
> > > > first to spring to mind.
> > > >
> > > > > > > It is more than just development. A devicetree is needed for binman to
> > > > > > > work, even if it is empty. The documentation idea doesn't really work,
> > > > > > > as I think I have proven by the difficulty in getting this series
> > > > > > > together. An automated mechanism that runs in CI might be acceptable,
> > > > > > > but that is in the future. For now, I believe it just HAS to be
> > > > > > > in-tree.
> > > > > >
> > > > > > I still don't see any reason why we need these incorrect and not
> > > > > > functionally used device trees in-tree when a dummy invalid tree is
> > > > > > enough to make things link.  We're dealing with real "we must have X.bin
> > > > > > in the output for things to function" issues on other platforms with
> > > > > > binman right now.  Using a dummy dts should be fine.
> > > > >
> > > > > Incorrect in what way?
> > > >
> > > > Well, in the QEMU instance, they're only as correct as the parameters
> > > > passed to qemu-system-foo when you did -dumpdtb to start with.  Lets
> > > > take TPM as that now should show up in the device tree, or not,
> > > > depending on if we have the backend side of it?  Or all of the examples
> > > > of how to arbitrarily configure a system as Heinrich noted.
> > > >
> > > > Or the Pi examples where we need to use the device tree passed to us
> > > > because config.txt is the official way to modify things in the device
> > > > tree on that platform.
> > >
> > > I feel like a lot of the confusion stems from the very different
> > > roles that U-Boot plays on various platforms:
> > > - In the traditional way U-Boot is the first and only piece of code
> > >   that runs between reset and the kernel. Having the DT as part of the
> > >   U-Boot image, and thus in the U-Boot source tree, makes sense, given
> > >   that we talk about a particular board only.
> > > - Many platforms run other pieces of software (TF-A, SCP firmware)
> > >   alongside or before U-Boot, but still U-Boot is the main attraction,
> > >   and is doing firmware and setup duties. Most cheap ARM SoCs (sunxi,
> > >   RK) fall under this category. Depending on the particular firmware
> > >   setup, having the DTs in the tree (as a copy of the canonical Linux
> > >   source) again makes sense, and the DTB should probably be part of the
> > >   built U-Boot image as well, unless there is some better place.
> > >
> > > But there is a quite different category of boards, where U-Boot is a
> > > mere *loader*, and UEFI provider. The heavy lifting of platform setup
> > > (clocks, DRAM, power) is either done by prior firmware code, or by a
> > > separate management processor. The RPis, ARM Juno boards, Highbank and
> > > many other (typically advanced) platforms fall under this category.
> > > U-Boot should be happy about the lesser burden, and just consume
> > > whatever DTB it finds in memory.
> > > Virtual/dynamic platforms like QEMU or the ARM FVP models also fall
> > > into this category: for a virtual platform hardware setup is mostly not
> > > needed (DRAM, clock gating), or the emulator takes care of this already.
> > >
> > > For all those platforms the DTB naturally lives with the other firmware
> > > bits already, or is even amended by them, and U-Boot should not try to
> > > duplicate this, especially when the hardware is somewhat dynamic.
> >
> > Yes that is all understood and have been bashed to death in various
> > threads. Still, it is not unreasonable, I think, for U-Boot to have a
> > way to use an in-tree devicetree for development and testing purposes.
> > It also reasonable, I think, to require some in-tree documentation
> > about how to get U-Boot running on the board.
>
> OK, but what at least I'm saying (and I think others are too), is that
> it's also not unreasonable to say that on some platforms that
> development and testing purpose might require the developer to enable
> things, rather than be the out of the box case (and may be more or less
> hard to do, depending on the platform).

Can we just say that *for now*, that is actually not acceptable and
we'll move to that model when we have our various pre-conditions
(bindings upstream, a central repo for DTs with easy downloading for
builds, automated validation) set up? I am trying to keep firmware
together and make it easy to build and understand.

Perhaps I can indicate how easy I'd like it to be. I'd like to build
the board in U-Boot. I'd like Binman (or whatever tool we end up with
here) to spit out a

- list of missing binaries along with instructions on where to get
them from / how to build them
- list of missing tools along with instructions on where to get them
from / how to build them

and once we have installed those once, we can build U-Boot again and
that platform successfully boots. Future iteration in U-Boot should be
simply a case of rebuilding U-Boot. Iteration in other projects should
just involve building that project, then running the packaging tool
again.

Regards,
Simon