Re: [PATCH 04/10] xen/arm: ffa: Fine granular call support

[Julien Grall <julien@xxxxxxx>]

On 23/09/2024 13:27, Jens Wiklander wrote:
> Hi,
Hi,

> On Sun, Sep 22, 2024 at 3:04 PM Julien Grall <julien@xxxxxxx> wrote:
> > Hi Bertrand,
> >
> > On 19/09/2024 14:19, Bertrand Marquis wrote:
> > > Create a bitmap to store which feature is supported or not by the
> > > firmware and use it to filter which calls done to the firmware.
> > >
> > > With this enabled. allow FF-A support to be activated for guest even if
> > Typo: s/./,/ I think.
> >
> > > the firmware does not support it.
> > Can you explain why you want to do this?
> >
> > The TEE mediator was designed to interpose with the HW. Without the HW
> > it doesn't entirely make sense to try to use it.
> >
> > It would also not work if the host system is using OP-TEE and expose to
> > some VM FF-A. So it feels that the mediator may not be the right place
> > to handle this case.
> That's a good point, but all the FF-A handling should be in the same
> module since there's bound to be code and state to share. The problem
> is that FF-A tries to be a TEE mediator while it's about to become
> more than that. We can work around it by probing the OP-TEE mediator
> first, but it's adding another exception or special case. Would it
> make sense to move the FF-A mediator out of the TEE mediator framework
> and establish it separately?
I don't particularly want to have the FF-A mediator out of the TEE 
mediator. At the moment, it is unclear to me how much of the SMC 
handling code can really be shared between a domain talking with the 
host firmware and an emulated version. Are we just going to end up to 
have "if firmware then to this else do that"?
Cheers,

--
Julien Grall