From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout-p-202.mailbox.org (mout-p-202.mailbox.org [80.241.56.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 30BFB2FD69D; Thu, 13 Nov 2025 11:34:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=80.241.56.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763033659; cv=none; b=oAw4Mrd9F3y27qgPB+z/8+lXkyBfPsAg3Pfw/odLv4XBLcZMyInNd5yklpGcf4Hu6fjDAi7sck7KkNgAcJDr3cqQtVH84fpQdF5Mcfb1bKQhOIBuNEatfF3HYrgMwUoICF8yBlcW3Tqe8khHAhfg4MNp+deCmvmuCicaBzPHC0o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763033659; c=relaxed/simple; bh=ua8dmVMKlKkuJrQ6eAXatkwp2khgLieidwCwNTGMUg0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=K9V+qt3iGeAFqlgc15ngyzbJDFGd7K8fHzZnSYErszpmngZdZXc9MUIyEVPnux6+Aj5nBjpno7YPKOf0+Lm5Oo++1sHU+N3NGv62wlhcXIxZarrSP97l9fAlnfAX0rjYADz4yd7pHj+9gLN+UdXEyvpq2o6Wa9xi0S+99B1PPPA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mailbox.org; spf=pass smtp.mailfrom=mailbox.org; dkim=pass (2048-bit key) header.d=mailbox.org header.i=@mailbox.org header.b=lkhjf2bu; arc=none smtp.client-ip=80.241.56.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mailbox.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=mailbox.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=mailbox.org header.i=@mailbox.org header.b="lkhjf2bu" Received: from smtp202.mailbox.org (smtp202.mailbox.org [10.196.197.202]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-202.mailbox.org (Postfix) with ESMTPS id 4d6dTC663Vz9t9s; Thu, 13 Nov 2025 12:34:07 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mailbox.org; s=mail20150812; t=1763033647; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=kstUxXctzALc3r6mHu6J3NJbeAPLhvcpKA5iAHi8E80=; b=lkhjf2bugBr8TeoCb0ZzOBM0DsINKupPBIdRwGnhRqoTv2mFtNO1B8+oWW3FtNoI1aR6Y5 lgCYLSgrWZLc1v01kB/g7qw/zsDs7iyvBDzg6yXJiwuFAk/k2i1+CxlG6HFK1/RtSv2H+1 WpKP4kIBl9vqND3Vuu/E88hm1AKtQKvSY7kwDlErNfF9HAWhJhpLiZK/Cg1GWkJEDXfVAH 02ujI/5S/pMV6GYs4RlT/tpeb5niqTrV4A6tB0mZ9LYLA+6DY5rDIGDAyID8JaNmQR0h/w Hb5zD+lQLV9yssY2mB7uoZOrg9Uih1isCNOWRrSEHkmSSs/moMZ+/PcbW2ndzw== Message-ID: <032bfb41-413d-4d59-aa66-7f109af4422d@mailbox.org> Date: Thu, 13 Nov 2025 12:34:03 +0100 Precedence: bulk X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH 1/2] dt-bindings: firmware: arm,scmi: Document arm,poll-transport property To: Cristian Marussi Cc: 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, Wolfram Sang , Geert Uytterhoeven , Laurent Pinchart References: <20251023123644.8730-1-marek.vasut+renesas@mailbox.org> <70554674-7020-4582-a4e7-dbee34907096@mailbox.org> <5ae0a793-d3e7-45d1-bf5c-3c46593d1824@mailbox.org> Content-Language: en-US From: Marek Vasut In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-MBO-RS-ID: e9d5488ffa9da467466 X-MBO-RS-META: e53boqqq1douzuw15mwdychamyjjxw4y On 11/13/25 12:03 PM, Cristian Marussi wrote: Hello Cristian, > bit of a late reply... No worries, I am buried under email myself, take your time. >>>> 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)... Thank you ! -- Best regards, Marek Vasut