Re: [PATCH edk2-platforms v2 1/1] Silicon/SynQuacer: add optional OP-TEE DT node

[Sumit Garg <sumit.garg@linaro.org>]

On Thu, 26 Jul 2018 at 13:20, Daniel Thompson
<daniel.thompson@linaro.org> wrote:
>
> On Thu, Jul 26, 2018 at 09:39:37AM +0200, Ard Biesheuvel wrote:
> > On 26 July 2018 at 09:36, Daniel Thompson <daniel.thompson@linaro.org> wrote:
> > > On Wed, Jul 25, 2018 at 12:04:58PM +0200, Ard Biesheuvel wrote:
> > >> On 23 July 2018 at 15:19, Sumit Garg <sumit.garg@linaro.org> wrote:
> > >> > OP-TEE is optional on Developerbox controlled via SCP firmware. To check
> > >> > if we need to delete OP-TEE DT node, we use DRAM1 region info as SCP
> > >> > firmware conditionally carves out Secure memory from DRAM1 region.
> > >> >
> > >> > Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > >> > Cc: Leif Lindholm <leif.lindholm@linaro.org>
> > >> > Contributed-under: TianoCore Contribution Agreement 1.1
> > >> > Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
> > >> > ---
> > >> >
> > >>
> > >> As discussed on IRC, i am not a fan of inferring the presence of
> > >> OP-TEE from the base/size values of the first DRAM region.
> > >>
> > >> Please refer to the existing PCIe code how to read a GPIO in PEI and
> > >> set a dynamic PCD accordingly, so you can use its value in
> > >> PlatformDxe.
> > >
> > > For Trusted Firmware I asked Sumit to look for the OP-TEE memory carve
> > > out rather than looking at the switches. This was based on concerns
> > > about version skew (new C-A53 firmware, old SCP firmware[1]), in particular
> > > if TF-A jumps to an OP-TEE that isn't actually loaded the system will
> > > fail in a not very transparent way (especially if the user hasn't found
> > > the debug UART behind the back panel yet).
> > >
> > > What is the consequence of passing a DT with OP-TEE present if one is
> > > not actually present? Do we at least get as far as bringing up the
> > > framebuffer before things explode?
> > >

If we pass a DT with OP-TEE and OP-TEE not present, Linux TEE generic
driver exits gracefully giving following message:

[    1.976021] optee: probing for conduit method from DT.
[    1.976033] optee: api uid mismatch

> >
> > Is there any way we can let OP-TEE supply a DT overlay?
>
> I guess it could implement a secure monitor call to provide it. In
> fact I find it a rather pleasing approach. However I think it still loops
> us round to pretty much the same question as before. Does TF-A "protec
> " a normal world that makes an SMC to an OP-TEE that isn't there by
> failing the call in a nice way?
>

TF-A returns SMC call for OP-TEE as unknown (error code: -1 in "x0"
register) if OP-TEE is not present.

-Sumit

>
> Daniel.