Hello Sudeep, On 01.03.22 16:12, Sudeep Holla wrote: > > Hi Ahmad, > > On Mon, Feb 28, 2022 at 05:01:39PM +0100, Ahmad Fatoum wrote: >> Hello Etienne, >> >> On 28.10.21 16:00, Etienne Carriere wrote: >>> Introduce compatible "linaro,scmi-optee" for SCMI transport channel >>> based on an OP-TEE service invocation. The compatible mandates a >>> channel ID defined with property "linaro,optee-channel-id". >> > > Not sure if Etienne's reply addressed your queries/concerns correctly. > I thought I will add my view anyways. > >> I just found this thread via the compatible in the STM32MP131 patch set: >> https://lore.kernel.org/all/20220225133137.813919-1-gabriel.fernandez@xxxxxxxxxxx/ >> >> Linux doesn't care whether PSCI is provided by TF-A, OP-TEE or something >> else, so there is just the arm,psci* compatible. >> > > Correct, the interface to the kernel is fixed and hence we must be able > to manage with the standard and fixed sole set of bindings for the same. > >> What's different about SCMI that this is not possible? Why couldn't the >> existing binding and driver be used to communicate with OP-TEE as secure >> monitor as well? >> > > However with SCMI, the spec concentrates and standardises all the aspects > of the protocol used for the communication while it allows the transport > used for such a communication to be implementation specific. It does > address some standard transports like mailbox and PCC(ACPI). However, > because of the flexibility and also depending on the hardware(or VM), > different transports have been added to the list. SMC/HVC was the one, > followed by the virtio and OPTEE. While I agree SMC/HVC and OPTEE seem > to have lot of common and may have avoided separate bindings. > > However the FIDs for SMC/HVC is vendor defined(the spec doesn't cover this > and hence we utilised/exploited DT). Some vendors wanted interrupt support > too which got added. OPTEE eliminates the need for FID and can also provide > dynamic shared memory info. In short, it does differ in a way that the driver > needs to understand the difference and act differently with each of the > unique transports defined in the binding. > > Hope that explains and addresses your concern. Thanks for the elaborate answer. I see now why it's beneficial to have an OP-TEE transport in general. I don't yet see the benefit to use it in the STM32MP13x instead of SMCs like with STM32MP15x, but that a discussion that I need to have in the aforementioned thread. Thanks again! Ahmad -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
