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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 07702CD5BC2 for ; Thu, 13 Nov 2025 11:03:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=MD5uXzVGGApG7p8HRtAp+gA1hKTXj4ZXoGDhCs//GoQ=; b=2p9JFt0FKxcgn+0a7DC/Q3olHV Tc85lx6eJ7wABtLbi9Q2rfvic1jIRJGamxwph3qAcnaYCdvo7U6Jod6uqg/wtocXb4/rvzXMHXr4f PI4vC90BQlkA3V0FQQ4XWqR++zTSqSOFQzsaYWyeqx2BszHEWW7m5Ft1DBMdjm6PQct9zm3NDjNRF FZV9SQ4EEvSmcPsfDoSePllNsFDA8ZN7o9P3JBu9zXGojY2EZNoYSt9lOOY4zi8sxc7UtGcU7n3p/ QHu8pol4cueLM63wViKjKKA/+4lwe5JZkYDDanZkvW9fSuhC+q4bRvZJDq1iPGTdreG3s5Vnr33ZY SKk7qy2A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vJV75-0000000AMGD-44jC; Thu, 13 Nov 2025 11:03:39 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vJV74-0000000AMFB-0wMD for linux-arm-kernel@lists.infradead.org; Thu, 13 Nov 2025 11:03:39 +0000 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 C9CDC12FC; Thu, 13 Nov 2025 03:03:29 -0800 (PST) Received: from pluto (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 11CCA3F66E; Thu, 13 Nov 2025 03:03:35 -0800 (PST) Date: Thu, 13 Nov 2025 11:03:33 +0000 From: Cristian Marussi To: Marek Vasut Cc: Cristian Marussi , arm-scmi@vger.kernel.org, Conor Dooley , Florian Fainelli , Krzysztof Kozlowski , Rob Herring , Sudeep Holla , devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-renesas-soc@vger.kernel.org Subject: Re: [PATCH 1/2] dt-bindings: firmware: arm,scmi: Document arm,poll-transport property Message-ID: References: <20251023123644.8730-1-marek.vasut+renesas@mailbox.org> <70554674-7020-4582-a4e7-dbee34907096@mailbox.org> <5ae0a793-d3e7-45d1-bf5c-3c46593d1824@mailbox.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5ae0a793-d3e7-45d1-bf5c-3c46593d1824@mailbox.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251113_030338_393199_0E816965 X-CRM114-Status: GOOD ( 29.33 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 30, 2025 at 01:52:42AM +0100, Marek Vasut wrote: > On 10/23/25 4:00 PM, Marek Vasut wrote: > > Hello again, > Hi, bit of a late reply... > > > On Thu, Oct 23, 2025 at 02:35:57PM +0200, Marek Vasut wrote: > > > > Document new property arm,poll-transport, which sets all SCMI > > > > operation into > > > > poll mode. This is meant to work around uncooperative SCP > > > > implementations, > > > > which do not generate completion interrupts. This applies > > > > primarily on mbox > > > > based implementations, but does also cover SMC and VirtIO ones. > > > > > > Hi, > > > > > > ..indeed I was thinking a while ago about exposing the existing > > > force- polling > > > switch but in my case it was purely a testing-scenario > > > configuration, so a > > > no-no for the DT, things are different if you have to describe an HW > > > that has > > > no completion IRQ also on the a2p channel... > > > > Correct, at least until the SCP on this hardware is updated. > > > > > ...having said that, though, usually polling-mode is reserved to a few > > > selected commands in a few chosen scenarios (as you may have seen), > > > 'carpet-polling' non-for-testing for all the commands on A2P seems a lot > > > inefficient and heavy...is it really a viable solution ? or these > > > systems use such a low rate of SCMI messages that polling after each and > > > every message is negligible ? > > > > > > ..just to understand the context... > > > > These systems are early in development and it is likely that the SCP > > will be updated to generate interrupts properly. Currently, this is not > > the case, hence the carpet-polling, until this is resolved. > > While I was going through the SCMI spec, DEN0056F , page 209 , section "4.1 > Shared memory based transport" , bullet • Completion interrupts, I found it > explicitly states: > > " > This transport supports polling or interrupt driven modes of communication. > In interrupt mode, when the callee completes processing a message, it raises > an interrupt to the caller. Hardware support for completion interrupts is > optional. > " Oh, yes...I knew that...it is just that till now, no systems were really ever developed that lacked the completion IRQ as a whole, it was, till now, more of a case of having the capability NOT to use it selectively at runtime and instead use polling when wanted (like for clock ops in ISR context) I am not sure what is the reason why this only-polling scenario was never supported in the HW description, this indeed pre-dates my work on SCMI.... ...I would/will check with Sudeep, when he's back, what are the reasons for this (if any)... Thanks, Cristian