Hi Jens, On Tue, Aug 01, 2023 at 02:28:34PM +0200, Jens Wiklander wrote: > > > > > > > ... > > > > > > > Changelog: > > > > > > > =============== > > > > > > > > > > > > > > v17: > > > > > > > > > > > > > > * show a debug message rather than an error when FF-A is not > > > > > > > detected > > > > > > [snip] > > > > > > > diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig > > > > > > > index c5835e6ef6..8fbadb9201 100644 > > > > > > > --- a/lib/efi_loader/Kconfig > > > > > > > +++ b/lib/efi_loader/Kconfig > > > > > > > @@ -55,13 +55,53 @@ config EFI_VARIABLE_FILE_STORE > > > > > > > stored as file /ubootefi.var on the EFI system partition. > > > > > > > > > > > > > > config EFI_MM_COMM_TEE > > > > > > > - bool "UEFI variables storage service via OP-TEE" > > > > > > > - depends on OPTEE > > > > > > > + bool "UEFI variables storage service via the trusted world" > > > > > > > + depends on OPTEE && ARM_FFA_TRANSPORT > > > > > > > > > > > > You didn't get my changes in here however. If you can do > > > > > > EFI_MM_COMM_TEE > > > > > > without ARM_FFA_TRANSPORT (as lx2160ardb_tfa_stmm_defconfig does) > > > > > > then > > > > > > you don't make this option depend on . If FF-A is only > > > > > > for use here, you make FF-A depend on this, and the FF-A specific > > > > > > variable depend on ARM_FFA_TRANSPORT. > > > > > > > > > > Abdellatif hinted at what's going on here. When I added this Kconfig > > > > > option to lx2160 FF-A wasn't implemented yet. > > > > > > > > The defconfig has existed since May 2020, which is when you added > > > > EFI_MM_COMM_TEE itself too. So I think it's that no one did the check I > > > > did until now and saw this series was disabling what was on the other > > > > platform. > > > > > > > > > Since FF-A isn't a new > > > > > communication mechanism but builds upon the existing SMCs to build an > > > > > easier API, I asked Abdellatif to hide this complexity. > > > > > We had two options, either make Kconfig options for either FF-A or the > > > > > traditional SMCs and remove the dependencies, or piggyback on FF-As > > > > > discovery mechanism and make the choice at runtime. The latter has a > > > > > small impact on code size, but imho makes developers' life a lot > > > > > easier. > > > > > > > > I'm not sure how much you can do a run-time option here since you're > > > > setting a bunch of default values for FF-A to 0 in Kconfig. If we're > > > > supposed to be able to get them at run time, we shouldn't need a Kconfig > > > > option at all. I'm also not sure how valid a use case it is where we > > > > won't know at build time what the rest of the firmware stack supports > > > > here. > > > > > > > > > > That's a fair point. FF-A in theory has APIs to discover memory. > > > Abdellatif, why do we need the Kconfigs for shared memory on FF-A? > > > > The statically carved out MM shared buffer address, size and offset cannot > > be discovered by FF-A ABIs. > > The MM communication driver in U-Boot could allocate the buffer and share > > it with the MM SP but > > we do not implement that support currently in either U-Boot or UEFI. > > > > Simon suggested we use build configs to set the buffer address, size and > > offset since we don't want > > a DT node for the MM firmware. > > In the OP-TEE driver we're allocating memory to share dynamically > using malloc() or memalign(). Why isn't the same approach possible > here? >
FF-A memory sharing can not be used because the MM SP needs to know the layout of the MM communication buffer during initialisation. This happens before the Normal world has got a chance to run. So we have a chicken and egg and Normal World cannot use FF-A ABIs to share the buffer as things stand. Cheers, Abdellatif
