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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1CC79C433EF for ; Fri, 22 Apr 2022 00:21:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1382407AbiDVAYQ (ORCPT ); Thu, 21 Apr 2022 20:24:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38870 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229784AbiDVAYP (ORCPT ); Thu, 21 Apr 2022 20:24:15 -0400 Received: from mailgw02.mediatek.com (unknown [210.61.82.184]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8C08F4968A; Thu, 21 Apr 2022 17:21:19 -0700 (PDT) X-UUID: 6bea87178aba4b2aa56d28a4144152af-20220422 X-CID-P-RULE: Release_Ham X-CID-O-INFO: VERSION:1.1.4,REQID:735316ce-94ac-4ebd-b6e8-18a33047e259,OB:0,LO B:0,IP:0,URL:8,TC:0,Content:0,EDM:0,RT:0,SF:0,FILE:0,RULE:Release_Ham,ACTI ON:release,TS:8 X-CID-META: VersionHash:faefae9,CLOUDID:1a2087f0-da02-41b4-b6df-58f4ccd36682,C OID:IGNORED,Recheck:0,SF:nil,TC:nil,Content:0,EDM:-3,File:nil,QS:0,BEC:nil X-UUID: 6bea87178aba4b2aa56d28a4144152af-20220422 Received: from mtkexhb01.mediatek.inc [(172.21.101.102)] by mailgw02.mediatek.com (envelope-from ) (Generic MTA with TLSv1.2 ECDHE-RSA-AES256-SHA384 256/256) with ESMTP id 325809546; Fri, 22 Apr 2022 08:21:11 +0800 Received: from mtkcas10.mediatek.inc (172.21.101.39) by mtkmbs10n1.mediatek.inc (172.21.101.34) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id 15.2.792.15; Fri, 22 Apr 2022 08:21:10 +0800 Received: from mhfsdcap04 (10.17.3.154) by mtkcas10.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Fri, 22 Apr 2022 08:21:10 +0800 Message-ID: Subject: Re: [PATCH v2] i2c: mediatek: Optimize master_xfer() and avoid circular locking From: Qii Wang To: AngeloGioacchino Del Regno CC: , , , , , , , Date: Fri, 22 Apr 2022 08:21:09 +0800 In-Reply-To: <20220411132107.136369-1-angelogioacchino.delregno@collabora.com> References: <20220411132107.136369-1-angelogioacchino.delregno@collabora.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5-0ubuntu0.18.04.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-MTK: N Precedence: bulk List-ID: X-Mailing-List: linux-i2c@vger.kernel.org On Mon, 2022-04-11 at 15:21 +0200, AngeloGioacchino Del Regno wrote: > Especially (but not only) during probe, it may happen that multiple > devices are communicating via i2c (or multiple i2c busses) and > sometimes while others are probing asynchronously. > For example, a Cr50 TPM may be filling entropy (or userspace may be > reading random data) while the rt5682 (i2c) codec driver reads/sets > some registers, like while getting/setting a clock's rate, which > happens both during probe and during system operation. > > In this driver, the mtk_i2c_transfer() function (which is the i2c > .master_xfer() callback) was granularly managing the clocks by > performing a clk_bulk_prepare_enable() to start them and its inverse. > This is not only creating possible circular locking dependencies in > the some cases (like former explanation), but it's also suboptimal, > as clk_core prepare/unprepare operations are using mutex locking, > which creates a bit of unwanted overhead (for example, i2c trackpads > will call master_xfer() every few milliseconds!). > > With this commit, we avoid both the circular locking and additional > overhead by changing how we handle the clocks in this driver: > - Prepare the clocks during probe (and PM resume) > - Enable/disable clocks in mtk_i2c_transfer() > - Unprepare the clocks only for driver removal (and PM suspend) > > For the sake of providing a full explanation: during probe, the > clocks are not only prepared but also enabled, as this is needed > for some hardware initialization but, after that, we are disabling > but not unpreparing them, leaving an expected state for the > aforementioned clock handling strategy. > > Signed-off-by: AngeloGioacchino Del Regno < > angelogioacchino.delregno@collabora.com> > Tested-by: Nícolas F. R. A. Prado Reviewed-by: Qii Wang > --- > > v2: Fixed typos in commit description > > drivers/i2c/busses/i2c-mt65xx.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > >