Hi Simon, [...]
> > > >>>>>>>>>> +config OF_BLOBLIST > > > >>>>>>>>>> + bool "DTB is provided by a bloblist" > > > >>>>>>>>>> + help > > > >>>>>>>>>> + Select this to read the devicetree from the bloblist. > > > >>>>>>>>>> This allows > > > >>>>>>>>>> + using a bloblist to transfer the devicetree between > > > >>>>>>>>>> U-Boot phases. > > > >>>>>>>>>> + The devicetree is stored in the bloblist by an early > > > >>>>>>>>>> phase so that > > > >>>>>>>>>> + U-Boot can read it. > > > >>>>>>>>>> + > > > >>>>>>>>> > > > >>>>>>>>> I dont think this is a good idea. We used to have 4-5 > > > >>>>>>>>> different options > > > >>>>>>>>> here, which we tried to clean up and ended up with two very > > > >>>>>>>>> discrete > > > >>>>>>>>> options. Why do we have to reintroduce a new one? Doesn't > > > >>>>>>>>> that bloblist > > > >>>>>>>>> have a header of some sort? The bloblist literally comes from > > > >>>>>>>>> a previous > > > >>>>>>>>> stage bootloader which is what OF_BOARD is here for. So why > > > >>>>>>>>> can't we just > > > >>>>>>>>> read the header and figure out if the magic of the bloblist > > > >>>>>>>>> matches? > > > >>>>>>>> > > > >>>>>>>> No, OF_BOARD is a hack to allow boards to do what they like with > > > >>>>>>>> the FDT. > > > >>>>>>>> > > > >>>>>>>> This patch is a standard mechanism to pass the DT from one > > > >>>>>>>> firmware > > > >>>>>>>> phase to the next. We have spent quite a bit of time creating a > > > >>>>>>>> spec > > > >>>>>>>> for it, and we should use it. > > > >>>>>>> > > > >>>>>>> Where exactly am I objecting using the spec? Can you please > > > >>>>>>> re-read my email? > > > >>>>>>> I am actually pointing out we should use the spec *properly*. So > > > >>>>>>> instead of having a Kconfig option for the DT, which is pretty > > > >>>>>>> pointless, we should parse the bloblist. If the header defined > > > >>>>>>> by > > > >>>>>>> the *spec* is found, we should just search for the DT in there. > > > >>>>>>> What you are doing here, is take the spec, pick a very specific > > > >>>>>>> item > > > >>>>>>> that the list contains, and create a Kconfig option out of it. > > > >>>>>>> Which > > > >>>>>>> basically ignores the discoverable options of the bloblist. For > > > >>>>>>> example, that bloblist can also contain an entry to a TPM > > > >>>>>>> eventlog. > > > >>>>>>> Should we start creating Kconfig options for all the firmware > > > >>>>>>> handoff > > > >>>>>>> entries that are defined on that spec? > > > >>>>>> > > > >>>>>> OK so that is a different thing. What should it do if it expects > > > >>>>>> to find a bloblist but cannot? I want it to throw an error, > > > >>>>>> because I am trying to make the boot deterministic. What do you > > > >>>>>> think? > > > >>>>> > > > >>>>> That's fine by me. You can even put that under IS_ENABLED for the > > > >>>>> bloblist inside the existing OF_BOARD check. So I was thinking > > > >>>>> - If no bloblist is required in Kconfig options we do the hacks we > > > >>>>> used to > > > >>>>> - if bloblist is selected and the config option is OF_BOARD, throw > > > >>>>> an > > > >>>>> error and mention that the previous stage loader should hand over a > > > >>>>> DT > > > >>>>> > > > >>>>> Is that what you had in mind? > > > >>>> > > > >>>> Yes, that sounds good to me. > > > >>>> > > > >>>> But I still think we need an OF_BLOBLIST option to control whether > > > >>>> the > > > >>>> devicetree comes from there. > > > >>>> Otherwise we will end up with people > > > >>>> using OF_BOARD to work around it. We also have the SPL case which > > > >>>> does > > > >>>> not pass the DT in a bloblist...in fact SPL typically doesn't even > > > >>>> have the full DT. > > > >>> > > > >>> Wouldn't IS_ENABLED(BLOBLIST) || IS_ENABLED(SPL_BLOBLIST) be enough? > > > >>> Inside the OF_BOARD portion of the function, search for a bloblist if > > > >>> the option is enabled. If you can't find a bloblist and the DT within > > > >>> that bloblist, then error out > > > >> > > > >> Just my 2c here. > > > >> I think all options should be possible to disable. It means I can > > > >> imagine to > > > >> disable u-boot not to take care about DT provided from previous stage. > > > >> The same > > > >> is for TPM event log. IMHO every stage should have an option to simply > > > >> ignore > > > >> data pass from previous stage. I don't really mind how it is done but > > > >> there > > > >> should be an option to by purpose say to ignore the part of pass data. > > > > > > > > That would be done by disabling BLOBLIST. I don't think having a > > > > Kconfig to say > > > > "I want a bloblist, but I only want the DT from there" is reasonable > > > > (or for any other item the bloblist can carry). OF_BOARD means the > > > > DT will come from a previous stage loader. If bloblist is enabled then > > > > the DT must come from there. > > > > > > I don't agree on this. If bloblist is enabled and DT is passed SW should > > > have a > > > freedom to ignore it. > > > > > > At start everything is likely in sync but later stages before U-Boot can > > > stay at > > > certain version but there could be a need to update u-boot where DT from > > > previous stage could be broken. > > > > But you *can* ignore it and load a different one later. The only > > restriction is that if you compile u-boot with the assumption an early > > stage bootloader provides a DT you *must* find it. But we will still > > just keep 2 options in U-Boot of how you get a DT. > > A previous loader provided it or U-Boot provided it. Whether that > > comes from a bloblist or a register is irrelevant no ? > > I'm not sure what is being requested here, so I'll leave this as is for v2. Please don't. A few mails above there's a discussion of how I'd prefer things to look like, please have a look and let me know if something isn't clear. tl;dr "That's fine by me. You can even put that under IS_ENABLED for the bloblist inside the existing OF_BOARD check. So I was thinking - If no bloblist is required in Kconfig options we do the hacks we used to - if bloblist is selected and the config option is OF_BOARD, throw an error and mention that the previous stage loader should hand over a DT" > > The main struggle I have is how to tell whether you expect to > *receive* the DT in the bloblist, or expect it to be attached to the > image and be *sent* to the next phase. bloblist > > SPL - attached to image, send in bloblist > U-Boot proper - not attached to image, receive it from bloblist > > This is exactly the problem that is solved by the 'standard passage' > stuff [1] but that depends on Firmware Handoff and [2] which are not > ready yet... > > So I think what I have is the best we can do for now. We can avoid the extra complication in Kconfigs. The DT either comes from u-boot itself or from a previous stage loader. we don't need the extra "it comes from a bloblist". If they come from a previous stage loader and BLOBLIST *is* enabled, then just scan for the DT, if you don't find it error out. Thanks /Ilias > > Regards, > Simon > > [1] https://patchwork.ozlabs.org/project/uboot/list/?series=281465&state=* > [2] https://patchwork.ozlabs.org/project/uboot/list/?series=365719