From: Simon Glass sjg@chromium.org Date: Wed, 3 Nov 2021 10:45:42 -0600
Hi Tom,
On Wed, 3 Nov 2021 at 10:02, Tom Rini trini@konsulko.com wrote:
On Wed, Nov 03, 2021 at 09:22:58AM +0100, Mark Kettenis wrote:
From: Simon Glass sjg@chromium.org Date: Tue, 2 Nov 2021 19:20:51 -0600
Hi Mark,
On Wed, 27 Oct 2021 at 16:30, Mark Kettenis mark.kettenis@xs4all.nl wrote:
From: Simon Glass sjg@chromium.org Date: Wed, 27 Oct 2021 12:23:21 -0600
Hi François,
On Wed, 27 Oct 2021 at 09:14, François Ozog francois.ozog@linaro.org wrote: > > > > On Wed, 27 Oct 2021 at 16:08, Simon Glass sjg@chromium.org wrote: >> >> Hi François, >> >> On Tue, 26 Oct 2021 at 00:07, François Ozog francois.ozog@linaro.org wrote: >> > >> > Hi Simon >> > >> > Position unchanged on this series: adding fake dts for boards that generate their device tree in the dts directory is not good. If you have them in documentation the it is acceptable. >> >> I think we are going to have to disagree on this one. I actually used >> the qemu one in testing/development recently. We have to have a way to >> develop in-tree with U-Boot. It does not impinge on any of your use >> cases, so far as I know. > > I am not the only one in disagreement... You just saw Alex Bénée from Qemu saying the same thing. > I understand the advanced debug/development scenario you mention. > But locating the DT files in the dts directory is mis-leading the contributors to think that they need to compile the DT for the targeted platforms. > For your advanced scenario, you can still have the dts in the documentation area, or whatever directory (except dts). compile it and supply to U-Boot.
We have this situation with rpi 1, 2 and 3 and I don't believe anyone has noticed. U-Boot handles the build automatically. If you turn off OF_BOARD, it will use the U-Boot devicetree always so you know what is going on.
Until. The Raspberry Pi foundation releases a new firmware that configures the hardware differently such that the addresses in the U-Boot devicetree are wrong and nothing works anymore. Can't speak for the rpi 1, but this has happened in the past for the rpi 2 and 3 as well as more recently on the rpi 4.
So I update my SD card with a new private-binary bootloader and things stop working? I think I can narrow that one down :-)
We can add a message to U-Boot indicating where the devicetree came from, perhaps? That might be useful given everything that is going on.
As in this case, quite often in these discussions I struggle to understand what is behind the objection. Is it that your customers are demanding that devicetrees become private, secret data, not included in open-source projects? Or is it just the strange case of QEMU that is informing your thinking? I know of at least one project where the first-stage bootloader produces a devicetree and no one has the source for it. I believe TF-A was created for licensing reasons...so can you be a bit clearer about what the problem actually is? If a board is in-tree in U-Boot I would like it to have a devicetree there, at least until we have a better option. At the very least, it MUST be discoverable and it must be possible to undertake U-Boot development easily without a lot of messing around.
How many people are there out there that work on U-Boot that don't have a Linux source tree checked out? Even I have several of those lying around on my development systems and I am an OpenBSD developer ;).
So it is OK to have the DT in Linux but not in U-Boot? I don't even know what to say that. How does that square with your point above?
Ideally the DT's and DT binding would move out of the Linux tree and into a repository of their own. But until that is the case, the Linux tree is the source of truth.
Yes, and this is a long known and slowly in progress kinda-sorta thing. A few more people helping to review things, etc, are always appreciated by upstream.
I am not talking about disabling OF_BOARD, just making it *possible* to do so.
And I don't think it makes sense to do so on most boards that have OF_BOARD in their config.
It should probably close to never be done, unless it's some case where it's crazy-hard to update the device tree correctly for the platform. So it's not a problem on Pi as it's just on the FAT32 partition right there, it's not a problem on Apple M1 as ..however you do it.., and so on.
I can almost hear the argument from here about "but I'm doing some work for U-Boot and need to add..." and that's where we need to figure out what to do next. Yes, we likely need to have some bindings of our own, and developing those AND pushing them upstream will require iterating here. So the developer point of view of how do I whack things to supply my own is valid. But it's not the default use case. The default use case is building the firmware that users rarely see, because their system boots to the OS and they get down to using their system.
I believe that OF_BOARD needs to become a runtime option.
I'm looking at this from the perspective of the Apple M1. But please no. That would only tempt users to flip the switch resulting in a non-bootable system.
If not, there is no way to use the U-Boot deivcetree.
There is no way to use the U-Boot devicetree on these boards, because it is incomplete. And the code to fill in the missing bits lives somewhere else.
I cannot build it in-tree. I cannot make U-Boot use it. It's just a mess.
Correct. So putting the device tree in the U-Boot repository makes no sense.
So we are supposed to run dtc manually to ge tthe DT, then copy it manually, then deal with the include files it needs and the C preprocessing it needs for the bindings?
Of course not. The repository that contains the DT sources will have the infrastructure to do that for you.
We are making this 'odd' case into the main case. It isn't. If it becomes it one day, I hope we are in a better place with devicetree. Upstreaming bindings is one thing, but we need to develop and test, first.
And the way I test things is that I build the device tree, load it together with the U-Boot binary into m1n1 over serial or USB and run it.
I really don't understand why this is generating so much discussion. How can we get this moving?
Maybe because you're continuously telling is we're doing it wrong and must do it your way?
What is so wrong with having a devicetree in U-Boot for building?
This sounds like you want to make having a devicetree in the actual U-Boot a hard requirement. And that makes no sense to me for the Apple M1 systems.
Why are these boards so special? And what problem does it cause? The only one I have heard is confusion, which I think I have addressed.
They're not special; just different.