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 X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D79E0C4332B for ; Fri, 20 Mar 2020 12:20:55 +0000 (UTC) Received: from alsa0.perex.cz (alsa0.perex.cz [77.48.224.243]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 5E9AC2072C for ; Fri, 20 Mar 2020 12:20:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alsa-project.org header.i=@alsa-project.org header.b="bSQCZGLo" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5E9AC2072C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=alsa-devel-bounces@alsa-project.org Received: from alsa1.perex.cz (alsa1.perex.cz [207.180.221.201]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa0.perex.cz (Postfix) with ESMTPS id BF61317B2; Fri, 20 Mar 2020 13:20:03 +0100 (CET) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa0.perex.cz BF61317B2 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=alsa-project.org; s=default; t=1584706853; bh=JP0Wynzh89rZt1JAstIjFy1I5AH6fMYbvZc07MELZHA=; h=Date:From:To:Subject:References:In-Reply-To:Cc:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From; b=bSQCZGLoukhwvb2+oIOWMAiZ13Kq6y7FpmTj1U/A6zRli0SXvM9TvQU/d+OUnMhyf Pezu+KAtI568E50aWBCDV/+hjGnvyke4g74s7Rr2IrHEc2bBZUaiVBlw1VfE9+5vPP DAjx4sRoPZ+KR1L37io52yvDFGqHL/5OFz53nYls= Received: from alsa1.perex.cz (localhost.localdomain [127.0.0.1]) by alsa1.perex.cz (Postfix) with ESMTP id 3EDCEF800C0; Fri, 20 Mar 2020 13:20:03 +0100 (CET) Received: by alsa1.perex.cz (Postfix, from userid 50401) id E9013F8015B; Fri, 20 Mar 2020 13:19:59 +0100 (CET) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by alsa1.perex.cz (Postfix) with ESMTP id 82B5CF800C0; Fri, 20 Mar 2020 13:19:55 +0100 (CET) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz 82B5CF800C0 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 4CE3331B; Fri, 20 Mar 2020 05:19:54 -0700 (PDT) Received: from localhost (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 01EE93F85E; Fri, 20 Mar 2020 05:19:53 -0700 (PDT) Date: Fri, 20 Mar 2020 12:19:52 +0000 From: Mark Brown To: Guennadi Liakhovetski Subject: Re: [PATCH 06/14] ASoC: SOF: add a power status IPC Message-ID: <20200320121952.GC3961@sirena.org.uk> References: <20200312144429.17959-1-guennadi.liakhovetski@linux.intel.com> <20200312144429.17959-7-guennadi.liakhovetski@linux.intel.com> <20200313143956.GJ5528@sirena.org.uk> <20200320115203.GA2130@ubuntu> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="1SQmhf2mF2YjsYvc" Content-Disposition: inline In-Reply-To: <20200320115203.GA2130@ubuntu> X-Cookie: Laugh when you can User-Agent: Mutt/1.10.1 (2018-07-13) Cc: Liam Girdwood , Takashi Iwai , alsa-devel@alsa-project.org, sound-open-firmware@alsa-project.org X-BeenThere: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" --1SQmhf2mF2YjsYvc Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Mar 20, 2020 at 12:52:03PM +0100, Guennadi Liakhovetski wrote: > On Fri, Mar 13, 2020 at 02:39:56PM +0000, Mark Brown wrote: > > On Thu, Mar 12, 2020 at 03:44:21PM +0100, Guennadi Liakhovetski wrote: > > > #endif > > > + atomic_set(&sdev->reset_count, 0); > > > dev_set_drvdata(dev, sdev); > > Do we really need to use atomics for this? They are hard to use > > correctly. > This variable is accessed from 2 contexts: it's incremented by the SOF=20 > driver, when the firmware has booted and it's read by the SOF > VirtIO backend vhost-be.c when receiving a resume request from the guest.= =20 > Timewise the variable will only be incremented during the DSP resume /=20 > power up, while the VirtIO back end is waiting for the resume to complete= in=20 > pm_runtime_get_sync(). And only after that it reads the variable. But tha= t=20 > can happen on different CPUs. Whereas I think that runtime PM will sync= =20 > caches somewhere during the process, I think it is better to access the= =20 > variable in an SMP-safe way, e.g. using atomic operations. That doesn't address my concern - to repeat, my concern is that atomics are hard to use correctly. Is there no other concurrency primitive (for example this sounds like a completion) which can be used? --1SQmhf2mF2YjsYvc Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAl50tOcACgkQJNaLcl1U h9Clxgf/TuSaiB+A2YdysduRHryPVrTF9qdkgGFux2O8/4ddyE2Rbtn6qNVoBebz K1dH1Unb6Lgwt8yjwiE+q195f9XZbxUoXMiarb/bXLmUhzmsvjSaMK5Udrza+S2V tIxaeX14r0FdpbFoF0AEUBrRfxuNIZiL9ozx/0VDxOFtETed7BnnwmgIEJ40qvkl 6eQYyml4xOfsupfnSwwTu5f3omvX+vl28Q7dNv1mVZhh2Ksk6kGByuzNkg87rTZR PTY3OeEFXHb7X3sByZdriQaQLmsNHZkesnEScaU9Cw/96ufH2TdUPt1WqsMRE5K7 DCYJajK/2NGjUXqp+9bh34RlAuHzrw== =PaZL -----END PGP SIGNATURE----- --1SQmhf2mF2YjsYvc--