Hi Tom, On Sat, 4 Dec 2021 at 11:03, Tom Rini <tr...@konsulko.com> wrote: > > On Sat, Dec 04, 2021 at 08:20:55AM -0700, Simon Glass wrote: > > Hi Tom, > > > > On Sat, 4 Dec 2021 at 06:52, Tom Rini <tr...@konsulko.com> wrote: > > > > > > On Fri, Dec 03, 2021 at 06:01:56PM -0700, Simon Glass wrote: > > > > > > [huge snip] > > > > > There's things that need to be cleaned up because we have some small > > > > > number of platforms that went off and did their own thing. But > > > > > largely > > > > > yes, things make sense to me. We have: > > > > > - We embedded the device tree that will configure U-Boot, because > > > > > there > > > > > is no way for the hardware to have provided us one. > > > > > - We do not embed the device tree that will configure U-Boot, because > > > > > there is already one present in memory for us to use. > > > > > > > > > > Then we have the developer option of: > > > > > - We embedded the device tree that will configure U-Boot, because > > > > > we're > > > > > developing something. > > > > > > > > Yes, agreed those are the cases. To me this needs to be a run-time > > > > choice. > > > > > > But it's not possible. That's the problem we keep going around and > > > around about. People keep raising real life examples where you cannot > > > make a run time choice between "device tree we're passed at run time" > > > and "device tree we're compiled with". > > > > I haven't seen one. The most extreme case is QEMU and it works fine. I > > even added a test with it. What am I missing? > > QEMU and Xen should both never have an in-source-tree dts as they are > dynamic. I think you missed the explanation about how U-Boot + Xen > works? You're running the same U-Boot under Xen on any arbitrary ARMv8 > (with required features...) system. For QEMU virtual machines you're > not supposed to do what you're doing, for production. > > > > And it's not helpful. It is ALWAYS the case that we know that we want > > > to override the run time device tree with our own, because it's a > > > developer developing things or it's a user / production case where we > > > must use the provided tree. NOT doing that is what leads to madness > > > like we see for example on Pi where if we don't use the passed tree we > > > still need to copy X/Y/Z out of it. > > > > Aren't you talking about the distro DT there, rather than the the one > > on the boot disk? That is my reading of that patch. If we need to do > > that sort of thing, it doesn't matter where the the cointrol DT comes > > from. You are still going to have to do that sort of thing. > > > > It is not ALWAYS the case. I've shown you how easy it is to disable > > OF_BOARD and still boot / iterate. > > The DT we're passed in is the DT to pass to the OS. That's the hook for > putting a DTB on the device as it ships, the OS will just work. The > production case of needing to update that stored DTB is handled. It's > always what should be used, again outside of developer doing > development. > > Maybe that's part of the confusion here too. The DTB U-Boot is using is > the DTB the OS will consume too, in the passed at run time case. Unless > we're instead going to save that DTB aside? Which leaves me with a > different set of design questions... > > > > > > > Are you looking to have an empty DT in u-boot.bin? Perhaps we should > > > > > > provide a way to do that? But what is driving that desire? > > > > > > > > > > I'm looking for ways to convince you that we do not need to include a > > > > > device tree in the binary. There's a growing set of devices where the > > > > > device tree exists with the device. If it's missing, that's a huge > > > > > fatal error we can't do all that much about. If we need to do > > > > > something > > > > > to that device tree for U-Boot, yes, fine, we should make it straight > > > > > forward for the developer to do that. But that's not the common case! > > > > > > > > Well we could add another Kconfig which tells U-Boot not to include a > > > > devicetree in u-boot.bin, if that would resolve this? > > > > > > > > I just want to make sure that we always build the devicetrees and that > > > > it is easy for a knowledgeable dev to switch over to use them, without > > > > spelunking through dozens of other projects to discover the secret DT > > > > that no one will tell us about. > > > > > > Should we demand better documentation for boards? Yes. But it's still > > > a valid case to have zero device trees for a given platform in-tree. > > > Xen is an example of this. QEMU is an example of this. Platforms need > > > to work without adding special tweaks for us. Maybe that means some > > > features can't be tested in QEMU-as-virtual-platform and only in > > > QEMU-faithfully-emulating-specific-physical-platforms. > > > > You mention QEMU (for ARM and RISC-V) and now XEN. They are a special > > case, I think. How about we create a special Kconfig for that case? We > > need to make some progress here. > > Yes, because there's a small number of OF_BOARD=y configs in tree right > now, most of which are QEMU virtual machines, others of which are Pi > (which we've talked to death), highbank (which Andre has explained), and > then the octeontx stuff I don't know how works. I keep pushing to say > that OF_BOARD=y is the special case we need to not overrule the device > tree provided to us on. Unless we start saving off that passed-to-us DTB > and then something-something for our own run-time DTB, and letting the > OS consume that passed-to-us one with only normal fixups applied. > > > > > > I guess another part of the problem is that historically almost all > > > > > platforms were in the first case I list above, no run time provided > > > > > device tree, so we took the kernel one and added our bindings to it. > > > > > Now we're being bit by the growing number of platforms that are the > > > > > second case, and how do we get our properties in there, and which ones > > > > > even make sense to do that for. > > > > > > > > I think upstreaming the bindings is the solution there. I've made a > > > > start, but we need to make progress with this series and all the other > > > > things in flight. I think a lot of people want U-Boot to not have a > > > > devicetree source files in it for ARMv8 platforms. I am strongly > > > > opposed to that. I've laid out my reasons very clearly in the past. I > > > > think this is a good summary: > > > > > > > > https://lists.gnu.org/archive/html/qemu-devel/2021-10/msg03480.html > > > > > > Yes, there are some ARMv8 platforms we will have to have the source > > > files to, in tree, because they won't come to us at run time. But > > > others we won't for practical reasons, namely that we can't statically > > > provide something that exists dynamically without massive duplication of > > > code or just taking things from that passed to us tree. > > > > So let's require that the static ones have the Linux DT in our tree > > for now. The dynamic ones are just QEMU for ARM and Xen, I think. If > > that's it then I can agree a special case for them, so long as we sort > > out the docs for Xen. > > I'm agreeable to saying that if the dts files exist in Linux (or other > official source locations) we should have those in-tree, and the board > maintainer doesn't object, yes. But I think that might be a slightly > different list than what you say here. And that punts the run-time > decision down the road. And I'm assuming you're OK with also not > including a dtb in the image. > > > > > I believe I have been consistent in this although with all the > > > > discussion I'm really not sure anymore. > > > > > > Yes, everyone has been consistent in these discussions. > > > > I'd like to think more people accept that U-Boot is allowed its own > > properties than did at the start. > > > > > > > > > The problem is that various people have various views about how U-Boot > > > > should work with devicetree. I strongly believe that until we have > > > > bindings upstream, a central repo for DTs with easy downloading for > > > > builds, automated validation, among other things, we must maintain the > > > > devicetree in U-Boot. Just from the POV of energy expended, I do not > > > > want to be arguing with the Linaro folks about what U-Boot is allowed > > > > to do every month for the next two years. I'd rather set out the stall > > > > now and then deal with the problems it causes from that perspective. > > > > > > The problems of the last going on 12 years won't be solved instantly. > > > The conflict as I see it is that you're insisting that all platforms > > > must have statically usable device trees, and I (and I believe others) > > > are saying that's unreasonable in cases where the trees are dynamic at > > > heart, lets just ensure we have good enough documentation for them, > > > which we don't today. > > > > > > To be clear and pick an example, I don't want Pi dts files in U-Boot, > > > but, OK, it's an easy enough case to sync them up and so long as we > > > aren't yet at the "now we pick at run time between compiled in or passed > > > to us dtb", I can accept them in tree, but not in the resulting binary > > > for OF_CONTROL=y. But as the Xen folks have also noted, there's no > > > reasonable tree to include there. It does need to be better documented > > > how to fire it up however, in our sources. > > > > I'm OK with us copying in the Linux devicetree and using that. But > > OF_BOARD must be a run-time option and able to be disabled. The > > devicetree must be built, so it is actually real. We can have a > > separate OF_OMIT or something like that to omit the devicetree from > > the output image, perhaps. > > You're changing the meaning of CONFIG options. I like the idea Mark > suggested (probably after you wrote this..) of introducing something new > for what you're talking about. But no, it's unreasonable to say that > every U-Boot binary will bundle one or more dtb and make a run time > decision about what to use as the normal way the world works. > > > All of the other things need to wait until we make progress with > > devicetree bindings, validation, > > > > How can we make progress on this? We have different goals, as I have > > explained, so we are not going to agree on everything. > > Replace patches 4 to 14 with syncing platforms dts files from current > Linux release, and when OF_BOARD=y don't include a device tree in the > resulting image? That might also need adding some documentation for > some platforms on where the device tree is and how to extract it.
How about we create a new option for that, as we discussed on IRC a while back? After all, sandbox uses OF_BOARD. It doesn't mean OF_PRIOR_STAGE, just that we call board_fdt_blob_setup(). So something like OF_OMIT_DTB? For U-Boot as a whole this is an uncommon case. We also need to think about the protections again, perhaps we define OF_HAS_PRIOR_STAGE to indicate that the board works this way, then make it hard to disable OF_BOARD if that is set. Regards, Simon
