On Sun, Oct 22, 2023 at 11:31:52PM +0200, Heinrich Schuchardt wrote: > On 10/22/23 19:08, Tom Rini wrote: > > On Sun, Oct 22, 2023 at 06:34:08PM +0200, Heinrich Schuchardt wrote: > > > On 10/22/23 17:55, Tom Rini wrote: > > > > On Sun, Oct 22, 2023 at 10:47:33AM +0200, Heinrich Schuchardt wrote: > > > > > > > > > Forward and backward compatibility of Linux kernel device-trees is > > > > > sometimes missing. One solution approach is to load a kernel specific > > > > > device-tree. This can either be done via a U-Boot scripts (like the > > > > > one > > > > > generated by Debian package flash-kernel or by a boot loader like > > > > > GRUB. > > > > > The boot loader approach currently requires to know the device-tree > > > > > name > > > > > before first boot which makes it unusable for generic images. > > > > > > > > > > Expose the device-tree file name as EFI variable FdtFile. > > > > > This will allow bootloaders to load a kernel specific device-tree. > > > > > > > > > > The variable will not be exposed on ACPI based systems or if the > > > > > environment variable fdtfile is not defined. > > > > > > > > > > Signed-off-by: Heinrich Schuchardt <heinrich.schucha...@canonical.com> > > > > > --- > > > > > v3: > > > > > Add documentation > > > > > v2: > > > > > Use a unique GUID to enable future U-Boot independent > > > > > standardization. > > > > > Do not try to add the variable on ACPI based systems. > > > > > --- > > > > > doc/develop/uefi/uefi.rst | 17 +++++++++++++++++ > > > > > include/efi_loader.h | 5 +++++ > > > > > lib/efi_loader/efi_setup.c | 30 ++++++++++++++++++++++++++++++ > > > > > 3 files changed, 52 insertions(+) > > > > > > > > > > diff --git a/doc/develop/uefi/uefi.rst b/doc/develop/uefi/uefi.rst > > > > > index fb16ac743a..a81d09ae81 100644 > > > > > --- a/doc/develop/uefi/uefi.rst > > > > > +++ b/doc/develop/uefi/uefi.rst > > > > > @@ -916,6 +916,23 @@ So our final format of the FilePathList[] is:: > > > > > Loaded image - end node (0xff) - VenMedia - initrd_1 - [end > > > > > node (0x01) - initrd_n ...] - end node (0xff) > > > > > +EFI variable FdtFile > > > > > +~~~~~~~~~~~~~~~~~~~~ > > > > > + > > > > > +Ideally U-Boot would always expose a device-tree that can be used > > > > > for booting > > > > > +any operating systems. Unfortunately operating systems like Linux > > > > > sometimes > > > > > +break forward and backward compatibility. In this case there is a > > > > > need to load > > > > > +an operating system version specific device-tree. > > > > > + > > > > > +U-Boot has an environment variable fdtfile identifying the > > > > > device-tree file to > > > > > +load. The content of this variable is exposed as EFI variable > > > > > Fdtfile, vendor > > > > > +GUID d45dde69-3bd6-40e0-90d5-6b606aa57730. It contains the > > > > > device-tree path > > > > > +name as a NUL terminated ASCII string. > > > > > + > > > > > +On 32bit ARM this is currently only a file name, e.g. > > > > > 'imx6dl-wandboard.dtb'. > > > > > +On other architectures the file name is preceded by the vendor > > > > > directory, e.g. > > > > > +'rockchip/rk3326-odroid-go2.dtb'. > > > > > > > > The Linux Kernel has split 32bit ARM up by directory now, too. > > > > > > Since Linux v6.5. That is why I wrote "currently". Once we migrate the > > > values of $fdtfile in U-Boot we may want to change > > > distro_efi_try_bootflow_files() to search both with and without vendor > > > directory. > > > > > > Are there already plans for that migration? > > > > Right, v6.5 is out and has this change and v6.6 will be out soon enough, > > so the documentation we're adding here and now should be worded such > > that doesn't get stuck on these specifics. > > Should I add a sentence: > > Linux v6.5 has added vendor directories on 32bit ARM and U-Boot is expected > to follow suit.
No, please re-word the section to be more generic. Some architectures use vendor directories, some don't. I really don't know what we're going to do in U-Boot. -- Tom
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