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. > > 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 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. Regards, Simon
