Hi François, On Thu, 28 Oct 2021 at 02:21, François Ozog <francois.o...@linaro.org> wrote: > > Hi Simon, > > Le jeu. 28 oct. 2021 à 04:51, Simon Glass <s...@chromium.org> a écrit : >> >> Hi Ilias, >> >> On Tue, 26 Oct 2021 at 00:46, Ilias Apalodimas >> <ilias.apalodi...@linaro.org> wrote: >> > >> > Hi Simon, >> > >> > A bit late to the party, sorry! >> >> (Did you remember the beer? I am replying to this but I don't think it >> is all that helpful for me to reply to a lot of things on this thread, >> since I would not be adding much to my cover letter and patches) >> >> > >> > [...] >> > >> > > > >> > > > 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. >> > > >> > > 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 >> > > 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. >> > > >> > > (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 :-) >> > >> > Having U-Boot keep it's *internal* config state in DTs is fine. Adding >> > that to the DTs that are copied over from linux isn't imho. There are >> > various reasons for that. First of all syncing device trees is a huge pain >> > and that's probably one of the main reasons our DTs are out of sync for a >> > large number of boards. >> > The point is this was fine in 2011 were we had SPL only, but the reality >> > today is completely different. There's previous stage boot loaders (and >> > enough cases were vendors prefer those over SPL). If that bootloader needs >> > to use it's own device tree for whatever reason, imposing restrictions on >> > it wrt to the device tree it has to include, and require them to have >> > knowledge of U-Boot and it's internal config mechanism makes no sense not >> > to mention it doesn't scale at all. >> >> I think the solution here may be the binman image packer. It works >> from a description of the image (i.e. is data-driver) and can collect >> all the pieces together. The U-Boot properties (and the ones required >> by TF-A, etc.) can be added at package time. >> >> If you think about it, it doesn't matter what properties are in the DT >> that is put into the firmware image. TF-A, for example, is presumably >> reading a devicetree from flash, so what does it care if it has some >> U-Boot properties in it? > > > I am going to change my position in all mail threads I participate. > I was trying to make patches relevant in the future and conceptually clean. > That may not be the most effective position: I should just care about Linaro > and its members being able to implement SystemReady concepts. > > > If you mandate U-Boot has nodes in the device tree passed to the OS, we can > put DT fragment in the nt_fw_config section of the fip and merge it at boot > time. So there is a solution compatible with SystemReady. > > If you want to put fake, non future proof, DT sources in the dts for > platforms that are organized to provide the authoritative DT to U-Boot at > runtime, that's kind of your choice (hopefully representing the rest of > U-Boot community). There will be quirk code in U-Boot to redo the adaptations > on its non authoritative DT that the platform previous stage firmware does > (already saw one in the past month); as Mark said there will be issues over > time; and it will confuse people about the role of the DT. But I am fine with > it as it does not impair Linaro and its members ability to implement > SystemReady way of handling DT.
OK thank you. It doesn't sound like you are very on-board though. Also, you mischaracterise my intent with in-tree devicetrees. I would be happy enough for now if you could accept that U-Boot has nodes/properties of its own in the devicetree. It has been a feature of U-Boot for 10 years now. Regards, Simon > >> >> >> As to syncing, we have solved this using u-boot.dtsi files in U-Boot, >> so I think this can be dealt with. >> >> > >> > > >> > > 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. >> > > >> > >> > Again, the board might decide for it's own reason to provide it's own DT. >> > IMHO U-Boot must be able to cope with that and asking DTs to be included in >> > U-Boot source is not the right way to do that, not to mention cases were >> > that's completely unrealistic (e.g QEMU or a board that reads the DTB from >> > it's flash). >> >> I think you are at step 2. See above for my response. >> >> > >> > > (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. >> > >> > And that's exactly why we have to come up with something that scales, >> > without >> > having to add a bunch of unusable DTs in U-Boot. >> >> In what way does this not scale? How are the DTs unusable? If there is >> a standard binding, we should be fine. >> >> > >> > > 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. >> > >> > No we don't. That's a moot point. If you separate the DTs U-Boot >> > provides the internal one and inherits one 'generic'. Linux will be able >> > to use >> > that. So the only case were you'll need 3 DTs is if the *vendor* breaks >> > the >> > DT across kernel versions, In which case there's not much you can do to >> > begin with and that's already a case we have to deal with. >> >> Linux actually doesn't care if the U-Boot properties are in the tree, >> so long as we have proper bindings. My point here is we only need >> either: >> >> a. one devicetree, shared with Linux and U-Boot (and TF-A?) >> b. two devicetrees, one for use in firmware and one for passing to Linux >> >> We don't need to separate out the U-Boot properties into a second (or >> third) devicetree. There just isn't any point. >> >> > >> > > 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! >> > > >> > > 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? >> > >> > We can start slowly migrating boards and see how that works out. >> > We could either use 2 device trees as you proposed, or have u-boot merge >> > the 'u-boot' DTB and the inherited DTB before DM comes up. OTOH I'd prefer >> > if linux gets handed a clean device tree without the u-boot internals in >> > it, so I think 2 discrete DTs is cleaner overall. >> >> I know you would prefer that, but does it really matter in practice? >> What is the objection, actually? >> >> As I mentioned on the call, I think the prior stage should do any >> merging or fixing up. Trying to do that sort of thing in 'early' code >> in U-Boot (or any other program, including Linux) is such a pain. With >> U-Boot, for example, we don't even have any RAM available to do it >> with half the time and it would dramatically increase the amount of >> memory needed prior to relocation. It just isn't a very good idea to >> try to do this in early code. It is also completely unnecessary, once >> you get past the philosophical objections. >> >> If TF-A wants to be in the picture, let it deal with the implications >> and responsibility thus incurred. TF-A has no right to tell U-Boot how >> to handle its config. TF-A is 0.5m LOC, i.e. a lot, almost a quarter >> of the size of U-Boot. It duplicates loads of things in there. No one >> will even *notice* an FDT merge function, which is actually only 70 >> LOC: >> >> /** >> * overlay_apply_node - Merges a node into the base device tree >> * @fdt: Base Device Tree blob >> * @target: Node offset in the base device tree to apply the fragment to >> * @fdto: Device tree overlay blob >> * @node: Node offset in the overlay holding the changes to merge >> * >> * overlay_apply_node() merges a node into a target base device tree >> * node pointed. >> * >> * This is part of the final step in the device tree overlay >> * application process, when all the phandles have been adjusted and >> * resolved and you just have to merge overlay into the base device >> * tree. >> * >> * returns: >> * 0 on success >> * Negative error code on failure >> */ >> static int overlay_apply_node(void *fdt, int target, >> void *fdto, int node) >> { >> int property; >> int subnode; >> >> fdt_for_each_property_offset(property, fdto, node) { >> const char *name; >> const void *prop; >> int prop_len; >> int ret; >> >> prop = fdt_getprop_by_offset(fdto, property, &name, >> &prop_len); >> if (prop_len == -FDT_ERR_NOTFOUND) >> return -FDT_ERR_INTERNAL; >> if (prop_len < 0) >> return prop_len; >> >> ret = fdt_setprop(fdt, target, name, prop, prop_len); >> if (ret) >> return ret; >> } >> >> fdt_for_each_subnode(subnode, fdto, node) { >> const char *name = fdt_get_name(fdto, subnode, NULL); >> int nnode; >> int ret; >> >> nnode = fdt_add_subnode(fdt, target, name); >> if (nnode == -FDT_ERR_EXISTS) { >> nnode = fdt_subnode_offset(fdt, target, name); >> if (nnode == -FDT_ERR_NOTFOUND) >> return -FDT_ERR_INTERNAL; >> } >> >> if (nnode < 0) >> return nnode; >> >> ret = overlay_apply_node(fdt, nnode, fdto, subnode); >> if (ret) >> return ret; >> } >> >> return 0; >> >> >> >> } >> >> >> > >> > Regards >> > /Ilias >> > > >> > > 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. >> > > >> >> Regards, >> Simon