From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02F0BC433F5 for ; Tue, 8 Mar 2022 09:52:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229659AbiCHJxP (ORCPT ); Tue, 8 Mar 2022 04:53:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32788 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345520AbiCHJw5 (ORCPT ); Tue, 8 Mar 2022 04:52:57 -0500 Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5539841FA3 for ; Tue, 8 Mar 2022 01:52:01 -0800 (PST) Received: from gallifrey.ext.pengutronix.de ([2001:67c:670:201:5054:ff:fe8d:eefb] helo=[127.0.0.1]) by metis.ext.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1nRWVX-00065y-Ic; Tue, 08 Mar 2022 10:51:55 +0100 Message-ID: <2b4442d9-fb10-36ee-585d-4103b76abbbb@pengutronix.de> Date: Tue, 8 Mar 2022 10:51:54 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [PATCH v8 1/2] dt-bindings: arm: Add OP-TEE transport for SCMI Content-Language: en-US To: Sudeep Holla Cc: Etienne Carriere , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Cristian Marussi , Vincent Guittot , devicetree@vger.kernel.org, Rob Herring , Pengutronix Kernel Team References: <20211028140009.23331-1-etienne.carriere@linaro.org> <58a0e791-9573-99c2-0cc5-3920a1048113@pengutronix.de> From: Ahmad Fatoum In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 2001:67c:670:201:5054:ff:fe8d:eefb X-SA-Exim-Mail-From: a.fatoum@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: devicetree@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org 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@foss.st.com/ >> >> 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 |