On Tue, Jul 20, 2021 at 08:45:59AM +0200, Jens Wiklander wrote: > On Tue, Jul 13, 2021 at 1:12 PM Sudeep Holla <sudeep.holla@xxxxxxx> wrote: > > > > On Fri, Jul 09, 2021 at 08:05:57AM +0000, Etienne CARRIERE wrote: > > > Hello Sudeep and all, > > > > > > On Wed, 7 Jul 2021 at 19:52, Sudeep Holla <sudeep.holla@xxxxxxx> wrote: > > > > > > > > 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? > No I was just mentioning that this patch series addresses notifications from secure world(optee in this case) which is very similar to what FF-A is trying to address too. Anyways, you brought up interesting idea of hybrid model, it would be good if that is possible and the specification allows for that. I don't think it does in the current form, may need some amendments to allow that I think. > > > > > > > > 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. > I understand. I was trying(ineffectively) to tell why it is not so trivial to use SGI and how FF-A is enabling that. On SPI, so it is expected that platform has SPI available for this ? > > > > > > > > On Wed, Jul 07, 2021 at 11:22:23AM +0530, Sumit Garg wrote: > > > > > On Tue, 6 Jul 2021 at 18:16, Marc Zyngier <maz@xxxxxxxxxx> wrote: > > > > > > > > [...] > > > > > > > > > > > > > > > > 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. > Yes, I was referring to addition of notification support in both worlds. I was trying to emphasize that both OPTEE and FF-A needs changes in the secure world. OPTEE changes could be small compared to starting with FF-A but it may result in deviation in notification hadling(in both worlds). > > > > > > 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. > > > > > 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. > > > > > 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. > Fair enough. > 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. > Sure, as long as that is conveyed to the adopters of this, it should be fine. Do you have plans to disable this feature for armv8-a ? I see that as safe approach to avoid any kind of conflicts. I just don't want similar arguments used as excuse on armv8-a. -- Regards, Sudeep
