On Tue, Jul 13, 2021 at 1:12 PM Sudeep Holla [off-list ref] wrote:

On Fri, Jul 09, 2021 at 08:05:57AM +0000, Etienne CARRIERE wrote:

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Hello Sudeep and all,

On Wed, 7 Jul 2021 at 19:52, Sudeep Holla [off-list ref] wrote:

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Hi Sumit,

I was holding off you reply as I didn't have all the background on this.
Achin did mention that this is preparatory work for FFA notifications.
I did mention to him that this is more than that, it is custom extension
to address what FF-A notification is trying to in standard way.

Are you suggesting that we should use a hybrid implementation with
FF-A for notifications and keep the rest as is for armv7-a?

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I share same opinion as Marc Z.

From what I've read in this thread this has mainly been about using
SGI notification and not whether asynchronous notification from OP-TEE
on non-FF-A systems is good or bad. I assume Sumit was asking about
SGI to find out why that wasn't used. This patch set uses SPI.

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On Wed, Jul 07, 2021 at 11:22:23AM +0530, Sumit Garg wrote:

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On Tue, 6 Jul 2021 at 18:16, Marc Zyngier [off-list ref] wrote:

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I don't care about OP-TEE. If you are proposing a contract between S
and NS, it has to be TEE and OS independent. That's how the
architecture works.

Agree, here we are not proposing a common contract among the S and NS
world that every TEE (based on Arm TrustZone) will use to communicate
with REE (Linux in our case) but rather an OP-TEE specific
notifications feature that is built on top of OP-TEE specific ABIs.

And I can see your arguments coming from an FFA perspective but there
are platforms like the ones based on Armv7 which don't support FFA
ABI. Maybe Jens can elaborate how this feature will fit in when FFA
comes into picture?

I can understand that but won't those platforms add the support both in
the kernel(current series) and secure world to address notifications.
While you could argue that it is small extension to what is already present
but I prefer they support FF-A is they need such a support instead of adding
custom mechanisms. It is hard to maintain and each vendor will deviate
from this custom mechanism and soon we will have bunch of them to handle.

Regarding deviation, are we still talking about the OP-TEE driver? So
far I haven't seen any vendor extensions at all in that driver.

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There exist armv7-a platforms that expect OP-TEE notification support and
will not move the FF-A, like the stm32mp15. This platform won't move to FF-A
mainly due to the memory cost of the added SPM layer and the device physical
constraints.

Fair enough on the use-case and the analysis for not being able to use FF-A.
As you may already know it doesn't simply this problem. This has been
discussed for years and FF-A was assumed to be the solution when FF-A
spec work started.

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We have a usecase for OP-TEE notification. We're working on the integration
of an SCMI server in OP-TEE. SCMI notification is a feature needed is this
scope and it requires OP-TEE async notification means as those proposed
here.

I am aware of this use-case, I understand. But I can only share rants
which I know doesn't help much.

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This OP-TEE async notif also brings a lot of value in OP-TEE as it allows a
OP-TEE secure thread (i.e. executing a trusted application service) to
gently wait on a secure interrupt (as a slow bus transaction completion or
many other usecase) with the CPU relaxed. This support is provided by the
proposed series. I believe existing device should be able to leverage this
OP-TEE feature without needing their OP-TEE to move to the new FF-A
interface.

While I agree these are nice to have in OPTEE, the timing is just odd.

We are trying hard to push FF-A as standard solution to address all such
issues that couldn't be solved with OPTEE + DT, now we are back to address
the same in parallel to FF-A.

It's not exactly the same since the primary target here is armv7-a
where introducing FF-A isn't an obvious choice in all cases. For
OP-TEE armv7-a is special in the way that all secure world processing
is handled by OP-TEE. The internal secure monitor already takes care
of what's implemented in TF-A at EL3 for armv8-a.

This isn't meant to compete with FF-A, it's to make sure that the
OP-TEE armv7-a user base isn't left behind. This doesn't rule out FF-A
support for armv7-a for those prepared to take that step.

Cheers,
Jens