On Fri, Oct 15, 2021 at 12:03:44PM -0600, Simon Glass wrote: > Hi all, > > On Thu, 14 Oct 2021 at 09:28, Tom Rini <tr...@konsulko.com> wrote: > > > > On Thu, Oct 14, 2021 at 09:17:52AM -0600, Simon Glass wrote: > > > Hi Tom, > > > > > > On Thu, 14 Oct 2021 at 08:56, Tom Rini <tr...@konsulko.com> wrote: > > > > > > > > On Wed, Oct 13, 2021 at 12:06:02PM -0600, Simon Glass wrote: > > > > > Hi François, > > > > > > > > > > On Wed, 13 Oct 2021 at 11:35, François Ozog > > > > > <francois.o...@linaro.org> wrote: > > > > > > > > > > > > Hi Simon > > > > > > > > > > > > Le mer. 13 oct. 2021 à 16:49, Simon Glass <s...@chromium.org> a > > > > > > écrit : > > > > > >> > > > > > >> Hi Tom, Bin,François, > > > > > >> > > > > > >> On Tue, 12 Oct 2021 at 19:34, Tom Rini <tr...@konsulko.com> wrote: > > > > > >> > > > > > > >> > On Wed, Oct 13, 2021 at 09:29:14AM +0800, Bin Meng wrote: > > > > > >> > > Hi Simon, > > > > > >> > > > > > > > >> > > On Wed, Oct 13, 2021 at 9:01 AM Simon Glass > > > > > >> > > <s...@chromium.org> wrote: > > > > > >> > > > > > > > > >> > > > 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 at [1]. > > > > > >> > > > > > > > > >> > > > 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. > > > > > >> > > > > > > > >> > > Adding device trees that are never used sounds like a hack to > > > > > >> > > me. > > > > > >> > > > > > > > >> > > For QEMU, device tree is dynamically generated on the fly > > > > > >> > > based on > > > > > >> > > command line parameters, and the device tree you put in this > > > > > >> > > series > > > > > >> > > has various hardcoded <phandle> values which normally do not > > > > > >> > > show up > > > > > >> > > in hand-written dts files. > > > > > >> > > > > > > > >> > > I am not sure I understand the whole point of this. > > > > > >> > > > > > > >> > I am also confused and do not like the idea of adding device > > > > > >> > trees for > > > > > >> > platforms that are capable of and can / do have a device tree to > > > > > >> > give us > > > > > >> > at run time. > > > > > >> > > > > > >> (I'll just reply to this one email, since the same points applies > > > > > >> to > > > > > >> all replies I think) > > > > > >> > > > > > >> I have been thinking about this and discussing it with people for a > > > > > >> few months now. I've been signalling a change like this for over a > > > > > >> month now, on U-Boot contributor calls and in discussions with > > > > > >> Linaro > > > > > >> people. I sent a patch (below) to try to explain things. I hope it > > > > > >> is > > > > > >> not a surprise! > > > > > >> > > > > > >> The issue here is that we need a devicetree in-tree in U-Boot, to > > > > > >> avoid the mess that has been created by OF_PRIOR_STAGE, OF_BOARD, > > > > > >> BINMAN_STANDALONE_FDT and to a lesser extent, OF_HOSTFILE. Between > > > > > >> Ilias' series and this one we can get ourselves on a stronger > > > > > >> footing. > > > > > >> There is just OF_SEPARATE, with OF_EMBED for debugging/ELF use. > > > > > >> For more context: > > > > > >> > > > > > >> http://patchwork.ozlabs.org/project/uboot/patch/20210919215111.3830278-3-...@chromium.org/ > > > > > >> > > > > > >> BTW I did suggest to QEMU ARM that they support a way of adding the > > > > > >> u-boot.dtsi but there was not much interest there (in fact the > > > > > >> maintainer would prefer there was no special support even for > > > > > >> booting > > > > > >> Linux directly!) > > > > > > > > > > > > i understand their point of view and agree with it. > > > > > >> > > > > > >> But in any case it doesn't really help U-Boot. I > > > > > >> think the path forward might be to run QEMU twice, once to get its > > > > > >> generated tree and once to give the 'merged' tree with the U-Boot > > > > > >> properties in it, if people want to use U-Boot features. > > > > > >> > > > > > >> I do strongly believe that OF_BOARD must be a run-time option, not > > > > > >> a > > > > > >> build-time one. It creates all sorts of problems and obscurity > > > > > >> which > > > > > >> have taken months to unpick. See the above patch for the rationale. > > > > > >> > > > > > >> To add to that rationale, OF_BOARD needs to be an option available > > > > > >> to > > > > > >> any board. At some point in the future it may become a common way > > > > > >> things are done, e.g. TF-A calling U-Boot and providing a > > > > > >> devicetree > > > > > >> to it. It doesn't make any sense to have people decide whether or > > > > > >> not > > > > > >> to set OF_BOARD at build time, thus affecting how the image is put > > > > > >> together. We'll end up with different U-Boot build targets like > > > > > >> capricorn, capricorn_of_board and the like. It should be obvious > > > > > >> where > > > > > >> that will lead. Instead, OF_BOARD needs to become a commonly used > > > > > >> option, perhaps enabled by most/all boards, so that this sort of > > > > > >> build > > > > > >> explosion is not needed. > > > > > > > > > > > > If you mean that when boards are by construction providing a DTB to > > > > > > U-Boot then I agree very much. But I don’t understand how the patch > > > > > > set supports it as it puts dts files for those boards to be built. > > > > > >> > > > > > >> U-Boot needs to be flexible enough to > > > > > >> function correctly in whatever runtime environment in which it > > > > > >> finds > > > > > >> itself. > > > > > >> > > > > > >> Also as binman is pressed into service more and more to build the > > > > > >> complex firmware images that are becoming fashionable, it needs a > > > > > >> definition (in the devicetree) that describes how to create the > > > > > >> image. > > > > > >> We can't support that unless we are building a devicetree, nor can > > > > > >> the > > > > > >> running program access the image layout without that information. > > > > > >> > > > > > >> François's point about 'don't use this with any kernel' is > > > > > >> germane...but of course I am not suggesting doing that, since > > > > > >> OF_BOARD > > > > > >> is, still, enabled. We already use OF_BOARD for various boards that > > > > > >> include an in-tree devicetree - Raspberry Pi 1, 2 and 3, for > > > > > >> example > > > > > >> (as I said in the cover letter "Most boards do provide one, but > > > > > >> some > > > > > >> don't."). So this series is just completing the picture by > > > > > >> enforcing > > > > > >> that *some sort* of devicetree is always present. > > > > > > > > > > > > That seems inconsistent with the OF_BOARD becomes the default. > > > > > > > > > > I think the key point that will get you closer to where I am on this > > > > > issue, is that OF_BOARD needs to be a run-time option. At present it > > > > > has build-time effects and this is quite wrong. If you go through all > > > > > the material I have written on this I think I have motivated that very > > > > > clearly. > > > > > > > > > > Another big issue is that I believe we need ONE devicetree for U-Boot, > > > > > not two that get merged by U-Boot. Again I have gone through that in a > > > > > lot of detail. > > > > > > > > I have a long long reply to your first reply here saved, but, maybe > > > > here's the biggest sticking point. To be clear, you agree that U-Boot > > > > needs to support being passed a device tree to use, at run time, yes? > > > > > > Yes. The OF_BOARD feature provides this. > > > > > > > > > > > And in that case, would not be using the "fake" tree we built in? > > > > > > Not at runtime. > > > > OK. > > > > > > So is the sticking point here that we really have two classes of > > > > devices, one class where we will never ever be given the device tree at > > > > run time (think BeagleBone Black) and one where we will always be given > > > > one at run time (think Raspberry Pi) ? > > > > > > I'm not sure it will be that black and white. I suspect there will be > > > (many) boards which can boot happily with the U-Boot devicetree but > > > can also accept one at runtime, if provided. For example, you may want > > > to boot with or without TF-A or some other, earlier stage. > > > > I'm not sure I see the value in making this a gray area. There's very > > much a class of "never" boards. There's also the class of "can" today. > > Maybe as part of a developer iterative flow it would be nice to not have > > to re-flash the prior stage to change a DT, and just do it in U-Boot > > until things are happy, but I'm not sure what the use case is for > > overriding the previous stage. > > > > Especially since the pushback on this series I think has all been "why > > are we copying in a tree to build with? We don't want to use it at run > > time!". And then softer push back like "Well, U-Boot says we have to > > include the device tree file here, but we won't use it...". > > See below. > > > > > > I believe we have got unstuck because OF_BOARD (perhaps inadvertently) > > > provided a way to entirely omit a devicetree from U-Boot, thus making > > > things like binman and U-Boot /config impossible, for example. So I > > > want to claw that back, so there is always some sort of devicetree in > > > U-Boot, as we have for rpi_3, etc. > > > > I really want to see what the binary case looks like since we could then > > kill off rpi_{3,3_b,4}_defconfig and I would need to see if we could > > then also do a rpi_arm32_defconfig too. > > > > I want to see less device trees in U-Boot sources, if they can come > > functionally correct from the hardware/our caller. > > > > And I'm not seeing how we make use of "U-Boot /config" if we also don't > > use the device tree from build time at run time, ignoring the device > > tree provided to us at run time by the caller. > > Firstly I should say that I find building firmware very messy and > confusing these days. Lots of things to build and it's hard to find > the instructions. It doesn't have to be that way, but if we carry on > as we are, it will continue to be messy and in five years you will > need a Ph.D and a lucky charm to boot on any modern board. My > objective here is to simplify things, bringing some consistency to the > different components. Binman was one effort there. I feel that putting > at least the U-Boot house in order, in my role as devicetree > maintainer (and as author of devicetree support in U-Boot back in > 2011), is the next step.
Yes, it's Not Great. I don't like my handful of build-BOARD.sh scripts that know where to grab other known-good binaries of varying licenses that are needed to assemble something that boots. > If we set things up correctly and agree on the bindings, devicetree > can be the unifying configuration mechanism through the whole of > firmware (except for very early bits) and into the OS, this will set > us up very well to deal with the complexity that is coming. > > Anyway, here are the mental steps that I've gone through over the past > two months: > > Step 1: At present, some people think U-Boot is not even allowed to > have its own nodes/properties in the DT. It is an abuse of the > devicetree standard, like the /chosen node but with less history. We > should sacrifice efficiency, expedience and expandability on the altar > of 'devicetree is a hardware description'. How do we get over that > one? Wel, I just think we need to accept that U-Boot uses devicetree > for its own purposes, as well as for booting the OS. I am not saying Yes, we need to have properties present in the device tree, and just like how "linux," is a valid vendor prefix for the linux kernel (but not used I would expect by the BSD families) we have cases that need "u-boot," properties. > it always has to have those properties, but with existing features > like verified boot, SPL as well as complex firmware images where > U-Boot needs to be able to find things in the image, it is essential. > So let's just assume that we need this everywhere, since we certainly > need it in at least some places. No, we can't / shouldn't assume we need this everywhere. A lot of places? Yes. But some features are going to be optional. A valid must be supported use case is something like a Pi where the hardware gives us a device tree, the tree is correct and some features in U-Boot aren't needed (SPL) nor possibly supported immediately (verified boot). We can go off on a tangent about how useful it would be to have HW platforms that are both common and can demonstrate a number of features, but that's its own problem to solve. > (stop reading here if you disagree, because nothing below will make > any sense...you can still use U-Boot v2011.06 which doesn't have > OF_CONTROL :-) > > Step 2: Assume U-Boot has its own nodes/properties. How do they get > there? Well, we have u-boot.dtsi files for that (the 2016 patch > "6d427c6b1fa binman: Automatically include a U-Boot .dtsi file"), we > have binman definitions, etc. So we need a way to overlay those things > into the DT. We already support this for in-tree DTs, so IMO this is > easy. Just require every board to have an in-tree DT. It helps with > discoverability and documentation, anyway. That is this series. > > (I think most of us are at the beginning of step 2, unsure about it > and worried about step 3) > > Step 3: Ah, but there are flows (i.e. boards that use a particular > flow only, or boards that sometimes use a flow) which need the DT to > come from a prior stage. How to handle that? IMO that is only going to > grow as every man and his dog get into the write-a-bootloader > business. We need a way to provide the U-Boot nodes/properties in a > form that the prior stage can consume and integrate with its build > system. Is TF-A the only thing being discussed here? If so, let's just > do it. We have the u-boot.dtsi and we can use binman to put the image > together, for example. Or we can get clever and create some sort of > overlay dtb. > > Step 3a. But I don't want to do that. a) If U-Boot needs this stuff > then it will need to build it in and use two devicetrees, one internal > and one from the prior stage....well that is not very efficient and it > is going to be confusing for people to figure out what U-Boot is > actually doing. But we actually already do that in a lot of cases > where U-Boot passes a DT to the kernel which is different to the one > it uses. So perhaps we have three devicetrees? OMG. b) Well then > U-Boot can have its own small devicetree with its bits and then U-Boot > can merge the two when it starts. Again that is not very efficient. It > means that U-Boot cannot be controlled by the prior stage (e.g. to get > its public key from there or to enable/disable the console), so > unified firmware config is not possible. It will get very confusing, > particularly for debugging U-Boot. c) Some other scheme to avoid > accepting step 3...please stop! How the nodes should get there is how the rest of the nodes in a system get there. Bindings are submitted and reviewed. The authoritative source of the dtses in question then has them, like any other property. > Step 4: Yes, but there is QEMU, which makes the devicetree up out of > whole cloth. What about that? Well, we are just going to have to deal > with that. We can easily merge in the U-Boot nodes/properties and > update the U-Boot CI scripts to do this, as needed, e.g. with > qemu-riscv64_spl. It's only one use case, although Xen might do > something similar. > > To my mind, that deals with both the build-time and run-time issues. > We have a discoverable DT in U-Boot, which should be considered the > source of truth for most boards. We can sync it with Linux > automatically with the tooling that I hope Rob Herring will come up > with. We can use an empty one where there really is no default, > although I'd argue that is making perfect an enemy of the good. > > Step 5: If we get clever and want to remove them from the U-Boot tree > and pick them up from somewhere else, we can do that with sufficient > tooling. Perhaps we should set a timeline for that? A year? Two? Six? These last two paragraphs condense what I think is honestly close to a decade of debate / discussion down to a fiat "U-Boot will have the DTS files". I don't want that. I don't think any of the other projects that want to leverage DTS files want that. > To repeat, if we set things up correctly and agree on the bindings, > devicetree can be the unifying configuration mechanism through the > whole of firmware (except for very early bits) and into the OS. I feel > this will set us up very well to deal with the complexity that is > coming. Sure, it could. But that doesn't mean that U-Boot is where the dts files live. -- Tom
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