Hi François, On Thu, 28 Oct 2021 at 08:50, François Ozog <francois.o...@linaro.org> wrote: > > Hi Simon > > Le jeu. 28 oct. 2021 à 16:30, Simon Glass <s...@chromium.org> a écrit : >> >> 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. > > On SystemReady systems the DT passed to U-Boot for the OS will be assembled > from the board DT and a U-Boot fragment/overlay. The board DT is free from > any software/firmware aspects, just contains hardware description. The U-Boot > fragment/overlay can contain any nodes it wants. The location of the bindings > specification is essentially irrelevant: it could be devicetree.org, U-Boot > doc or Linux kernel. Both DTs will be stored in the FIP. OEMs making their > firmware will just put whatever is needed in this “dynamic config” DT. On > SystemReady platforms U-Boot will always be given a DT, like on the RPI4. > U-Boot will be able to ignore it obviously. That said, doing so, a platform > may end-up failing compliance tests. > I think we need to document the above in U-Boot and refer to relevant > specifications. I’ll let Ilias propose something.
Hmm. So long as OF_BOARD is enabled, the devicetree will not be 'ignored'. Are you talking here about what TF-A will do? I assume so, since you mention FIP and I believe that is a TF-A invention. Of course the image is all packaged together in fact, so binman could presumably merge the DTs at build time, if desired. 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 > > -- > François-Frédéric Ozog | Director Business Development > T: +33.67221.6485 > francois.o...@linaro.org | Skype: ffozog >