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=-2.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,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 114B0C4332D for ; Fri, 20 Mar 2020 13:28:38 +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 8E7E62076E for ; Fri, 20 Mar 2020 13:28:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alsa-project.org header.i=@alsa-project.org header.b="c1yVeoje" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8E7E62076E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com 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 D579917C1; Fri, 20 Mar 2020 14:27:45 +0100 (CET) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa0.perex.cz D579917C1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=alsa-project.org; s=default; t=1584710915; bh=VoYc2JjgqX7sHXGVxqFBWeelREgL8vlillEjKoj4+ck=; h=Date:From:To:Subject:References:In-Reply-To:Cc:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From; b=c1yVeojeifI8gxnHmmzHppAUK1giErUuWiC+Npn6Zhsw90wuGAvfHQBdomQYW52U6 SUggf+4D0mRbWVFypxg9fl9tPoYpUg5pd9S7KzmEZO30vTOgw9yrPGA7VLgeDssSXJ 4hZYkAfACPDM84lmh9OSRLZYZgfZ97TlEOwUCawI= Received: from alsa1.perex.cz (localhost.localdomain [127.0.0.1]) by alsa1.perex.cz (Postfix) with ESMTP id 398C6F80126; Fri, 20 Mar 2020 14:27:45 +0100 (CET) Received: by alsa1.perex.cz (Postfix, from userid 50401) id 4D97AF8015B; Fri, 20 Mar 2020 14:27:43 +0100 (CET) Received: from mga17.intel.com (mga17.intel.com [192.55.52.151]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by alsa1.perex.cz (Postfix) with ESMTPS id C1F7DF80126; Fri, 20 Mar 2020 14:27:38 +0100 (CET) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz C1F7DF80126 IronPort-SDR: klgB8qQipJv7ApZhNKvut+816g5AdOxrJPogkyBHpqgJs/2hk4BP1/IF/DGR/9GZ5FJPsnQKJU jlWu42gNCrRA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Mar 2020 06:27:35 -0700 IronPort-SDR: yki/W19LjIwVCuym2ap7rDNaaT0kKsx3DVA77IkddL4ZLcvOwDNCpsDhfNaT95mZSOi7wwn2qW 2v3pXmTgRQcA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,284,1580803200"; d="scan'208";a="269088723" Received: from gliakhov-mobl2.ger.corp.intel.com (HELO ubuntu) ([10.252.57.199]) by fmsmga004.fm.intel.com with ESMTP; 20 Mar 2020 06:27:34 -0700 Date: Fri, 20 Mar 2020 14:27:33 +0100 From: Guennadi Liakhovetski To: Mark Brown Subject: Re: [PATCH 06/14] ASoC: SOF: add a power status IPC Message-ID: <20200320132732.GC2130@ubuntu> 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> <20200320121952.GC3961@sirena.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200320121952.GC3961@sirena.org.uk> 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" On Fri, Mar 20, 2020 at 12:19:52PM +0000, Mark Brown wrote: > 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 > > 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. > > Timewise the variable will only be incremented during the DSP resume / > > power up, while the VirtIO back end is waiting for the resume to complete in > > pm_runtime_get_sync(). And only after that it reads the variable. But that > > can happen on different CPUs. Whereas I think that runtime PM will sync > > caches somewhere during the process, I think it is better to access the > > 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? No, this isn't a completion - it's a counter. I've used atomic variables before, I cannot remember seeing any difficulties with their correct use described. Do you have a pointer? Thinking about it, one problem I see is wrapping, it isn't currently handled, but that would happen after quite a few PM suspend / resume cycles... Still it can and should be fixed. But this isn't the concern, that you have? Thanks Guennadi