On Thu, 2 Dec 2021 19:03:46 +0200 Ilias Apalodimas <ilias.apalodi...@linaro.org> wrote:
Hi, > On Thu, 2 Dec 2021 at 18:38, Tom Rini <tr...@konsulko.com> wrote: > > > > On Thu, Dec 02, 2021 at 05:33:53PM +0100, François Ozog wrote: > > > Hi Simon > > > > > > Le jeu. 2 déc. 2021 à 17:00, Simon Glass <s...@chromium.org> a écrit : > > > > > > > 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 in another patch in this > > > > series: "doc: Add documentation about devicetree usage" > > > > > > > > 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. > > > > > > > > Note: If board maintainers are able to add their own patch to add the > > > > files, some patches in this series can be dropped. > > > > > > > > It also provides a few qemu clean-ups discovered along the way. The > > > > qemu-riscv64_spl problem is fixed. > > > > > > > > [1] > > > > https://patchwork.ozlabs.org/project/uboot/patch/20210919215111.3830278-3-...@chromium.org/ > > > > > > > > Changes in v6: > > > > - Fix description of OF_BOARD so it refers just to the current state > > > > - Explain that the 'two devicetrees' refers to two *control* devicetrees > > > > - Expand the commit message based on comments > > > > - Expand the commit message based on comments > > > > > > You haven’t addressed any concerns expressed on the mailing list.so I am > > > not in favor of this new version either. > > > If you make a version without « fake DTs » as you name them, there are > > > good > > > advances in the documentation and other areas that would be better in > > > mainline…. > > > If I am the only one thinking this way and the patch can be accepted, I > > > would love there is a warning in capital letters at the top of the DTS > > > fake > > > files that explains the intent of this fake DT, the possible outcomes of > > > not using the one provided by the platform and the right way of dealing > > > with DTs for the platform. > > > > This is the part that I too am still unhappy about. I do not want > > reference or fake or whatever device trees in the U-Boot source tree. > > We should be able to _remove_ the ones we have, that are not required, > > with doc/board/...rst explaining how to get / view one. Not adding > > more. > > So this is a key point for me and the reason I completely disagree > with this approach. This proposal is working in the *exact* opposite > direction and we'll never be able to get rid of device trees from > U-Boot, even if at some point they move out of the kernel to a > 'common' repo'. I'll just repeat what I've been saying since v1. > Personally I'd be way happier if we could figure out were the specific > U-Boot config nodes are needed and when are they needed. Based on > what we figure out we could, pick up the device tree from a previous > state bootloader and fix it up with our special nodes before we start > using it, using internal DTS files (compiled to .dtbos or similar) > that indeed belong in the u-boot tree. I agree on that, I always felt like U-Boot is abusing the DT here for its own purposes. If it needs to convey some configuration information, it should do it separately. It can use the DTB *format* (hierarchically organised key/value pairs), but this should not really be mingled with the hardware information. Trusted-Firmware is using this idea: they use the already included libfdt for parsing, but load the various config "DTB"s separately. The "hw_config" DTB (as they call the actual DTB) is treated separately. Cheers, Andre
