From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3BB7D33858A; Thu, 13 Nov 2025 11:03:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763031819; cv=none; b=phPhqyso4e8YGeSO2FVh1xrpZtiYXy7euJU8evi1ZOdtEz4gtSNuJN6Ldi+yFAzifkvEyIWQoGYOAj1gxFXnSETgNR+OE8Gy+TuU2FA/HEulthr0lqoZ6nU9aOqP/ezPQB764FwVWYr4R2Kk1wmZO5hf1glZuo2RPyhS6ym+6uc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763031819; c=relaxed/simple; bh=3HHbn8SmWeQ7e6ONE8U1Lm7cOSkVRQmJs+OzzxqfvFM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ZnBVoCYh8ivY6IY4RNU3hmEly+1P8iSOZjfQULLpXbpAjpX3EgrPFEennJOUgqYWx9m/3hL++7wOIOE2OeX/4FJpRLsMQG3e9OAcfyvpRwqF17+vemQEM4iYjNEGs2TGuEViIQ4a9BlTUzTVuygJmapRSVsZO5hyWd3C7h1zucQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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> Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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> 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