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 C1E5EC433F5 for ; Fri, 4 Mar 2022 11:22:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239436AbiCDLXC (ORCPT ); Fri, 4 Mar 2022 06:23:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53798 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239477AbiCDLWx (ORCPT ); Fri, 4 Mar 2022 06:22:53 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 36B17137754; Fri, 4 Mar 2022 03:22:03 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 03CFC143D; Fri, 4 Mar 2022 03:22:03 -0800 (PST) Received: from bogus (e103737-lin.cambridge.arm.com [10.1.197.49]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DD2F03F70D; Fri, 4 Mar 2022 03:22:01 -0800 (PST) Date: Fri, 4 Mar 2022 11:21:59 +0000 From: Sudeep Holla To: Stefano Stabellini Cc: Cristian Marussi , Oleksii Moisieiev , Sudeep Holla , Krzysztof Kozlowski , "robh+dt@kernel.org" , "devicetree@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [RFC PATCH 0/1] dt-bindings: arm: Add scmi_devid paramter for Message-ID: References: <2546477f-4190-e838-3095-f47b31802445@kernel.org> <20220221213932.GA164964@EPUAKYIW015D> <7f17ab8f-429f-d2e0-8f5f-bfa2dd19cc49@kernel.org> <20220222161440.xadrgjftdyxenxgo@bogus> <20220222173458.GA2310133@EPUAKYIW015D> <20220224093232.GA12053@e120937-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 24, 2022 at 02:22:28PM -0800, Stefano Stabellini wrote: > On Thu, 24 Feb 2022, Cristian Marussi wrote: > > On Wed, Feb 23, 2022 at 06:51:59PM -0800, Stefano Stabellini wrote: > > > On Tue, 22 Feb 2022, Oleksii Moisieiev wrote: > > > > On Tue, Feb 22, 2022 at 04:14:40PM +0000, Sudeep Holla wrote: > > > > > On Tue, Feb 22, 2022 at 09:06:25AM +0100, Krzysztof Kozlowski wrote: > > > > > > On 21/02/2022 22:39, Oleksii Moisieiev wrote: > > > > > > > Hi Krzysztof, > > > > > > > > > > > Hi Stefano, > > > > > > > > > On Mon, Feb 21, 2022 at 10:01:43PM +0100, Krzysztof Kozlowski wrote: > > > > > > >> On 21/02/2022 18:26, Oleksii Moisieiev wrote: > > > > > > >>> Introducing new parameter called scmi_devid to the device-tree bindings. > > > > > > >>> This parameter should be set for the device nodes, which has > > > > > > >>> clocks/power-domains/resets working through SCMI. > > > > > > >>> Given parameter should set the device_id, needed to set device > > > > > > >>> permissions in the Firmware. This feature will be extremely useful for > > > > > > >>> the virtualized systems, which has more that one Guests running on the > > > > > > >>> system at the same time or for the syestems, which require several > > > > > > >>> agents with different permissions. Trusted agent will use scmi_devid to > > > > > > >>> set the Device permissions for the Firmware (See Section 4.2.2.10 [0] > > > > > > >>> for details). > > > > > > >>> Agents concept is described in Section 4.2.1 [0]. > > > > > > >>> > > > > > > >>> scmi_devid in Device-tree node example: > > > > > > >>> usb@e6590000 > > > > > > >>> { > > > > > > >>> scmi_devid = <19>; > > > > > > >>> clocks = <&scmi_clock 3>, <&scmi_clock 2>; > > > > > > >>> resets = <&scmi_reset 10>, <&scmi_reset 9>; > > > > > > >>> power-domains = <&scmi_power 0>; > > > > > > >>> }; > > > > > > >> > > > > > > >> And how do you prevent DT overlay adding such devid to any other node > > > > > > >> thus allowing any other device to send requests with given devid? > > > > > > >> > > > > > > > Thank you for the quick response. > > > > > > > scmi_devid value will be used only by Trusted Agent when the device > > > > > > > permissions are set. Non-trusted agents, which in our case are > > > > > > > represented as Guest OS are using scmi drivers, already present in linux > > > > > > > kernel, ignores scmi_devid and uses scmi_clocks, scmi_power, scmi_reset > > > > > > > nodes to access to SCMI protocol. > > > > > > > > > > > > Ah, ok. > > > > > > > > > > > > > > > > > > > >> Plus few technicalities: > > > > > > >> 1. Hyphen, not underscore in property name, so scmi-devid. > > > > > > > > > > > > > > Thanks for the tip, I will change that in v2. > > > > > > > > > > > > Few more thoughts: > > > > > > 1. This looks specific to ARM SCMI, so you also need vendor prefix, so > > > > > > something like: > > > > > > arm,scmi-devid > > > > > > arm,scmi-device-id > > > > > > > > > > > > > > > > Keeping the other discussion separate, I wanted to comment on this. > > > > > I agree with Krzysztof on having vendor specific prefix if we decide to add > > > > > this device id thing. However, I prefer not to use "arm,scmi-" here. > > > > > It can be "xen,scmi-" as we had plans to introduce some concepts in SCMI > > > > > spec that may use looks like this device-id. I would just like to avoid > > > > > conflicting with that in the future. It may happen to be same in the future > > > > > (i.e. this xen device-id matches 100% with definition of device-id we might > > > > > introduce in the spec, but I want to make assumption otherwise and leave > > > > > scope for divergence however small/little it can be). No issues even if > > > > > they converge and match 100% later in the far future. > > > > > > > > > > > > > xem,scmi- works for me. What do other thinks? > > > ^ xen,scmi- > > > > > > If this problem was Xen specific, then it would be fine to use xen,scmi- > > > As Xen developer, it solves my problem and I am fine with it. > > > > > > However, from a device tree and SCMI point of view, it looks like this > > > problem is generic and it just happens that Xen is the first > > > implementation to encounter it. > > > > > > Cristian wrote: "The SCMI spec does not indeed cover the discovery of > > > such devices and the related associated resources: it indeed delegates > > > such description to FDT/ACPI as of now." How is that supposed to happen > > > today with the current DT definitions, regardless of Xen? Is it a gap in > > > the current device tree binding? > > > > What I meant is that in fact SCMI device IDs are NOT needed in the Linux > > Kernel DT, in fact also this series does not add any code using it and > > there is no code as of now in Kernel to issue BASE_SET_DEVICE_PERMISSIONS > > commands; Linux Guest OS in the above scenario is a Non-Trusted agent and > > doesn't need to know SCMI DevIDs and must NOT have access to those IDs for > > security reasons too (as Sudeep was saying): the Trusted Agent (XEN here) > > and the SCMI platform server are the only ones required to share the > > knowledge of such Device IDs (and how the related resources are grouped) > > via some HW description scheme as you are doing indeed in XEN. > > > > So, while on one side such device IDs discovery is delegated by the spec > > to the HW description mechanisms, it seems just not needed in Kernel DT > > given the kind or role it has as an SCMI agent in this context: as said > > in fact there won't be any use as of now in Linux of such DT entries as > > of now. > > I see. This is one of those "difficult" cases where the device tree > binding is needed but it is not used by the Linux kernel. (We have a few > cases like this in system device tree and the more device tree gets > adopted by other projects the more will see instances like this one.) > Indeed, I mentioned this in the other email. It clearly falls under the larger umbrella of system device tree and not the one used by the Linux. > In that case, I think it is OK to call it "xen,scmi-" if Rob also > agrees. > Thanks. > After all, we are currently using in Xen a property called > "linux,pci-domain". We might as well have Linux in the future use a > property called "xen,scmi-devid" to even things out :-) Sure or we may add a generic one in the future as mentioned in the other email for reasons mentioned there. -- Regards, Sudeep