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 A268BC433EF for ; Thu, 21 Apr 2022 10:53:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1388593AbiDUK42 (ORCPT ); Thu, 21 Apr 2022 06:56:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39456 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1388575AbiDUK4V (ORCPT ); Thu, 21 Apr 2022 06:56:21 -0400 Received: from bhuna.collabora.co.uk (bhuna.collabora.co.uk [46.235.227.227]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 553351408C; Thu, 21 Apr 2022 03:53:32 -0700 (PDT) Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: kholk11) with ESMTPSA id B36F81F4558D DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1650538411; bh=FBd9UQCF3y8blk7MUJd+m6iRG4OWorxrv+jpCV+U8Mk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=KJkRBia6J5KzqsVbeppoDnuwy8hU/Tsp6FPN0BXe16JtWyGSs8OQBa2kd5BjM13fb mrub0DRmAYR4+hivTepMnAe/gbKHKzGqFBKZv+QKMmYU3A7c1QgZ25ozb9hMpfI6Qn zPEy9gcFNCXhnPZsyG+/+7NS1YyN/a9kjRy3I4oH7ygusMuDcCwgjSK0VCdPdNfhuE 56Pa1SruogNTZyC2oLrLXvCjcWFar5aC5gbqXfF6cMEON+rxEicQoRPpcN36KMVlum khBUmygJ0uZ/8UuDh1hVyJbL+B80kmBM0sEaKzRk2OFZgxyS+Y8IxdEioPNjRmBdT3 o8RKuMUzQpiqA== Message-ID: <4afda652-e360-cfd9-a0f5-07910b513621@collabora.com> Date: Thu, 21 Apr 2022 12:53:27 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH v2] i2c: mediatek: Optimize master_xfer() and avoid circular locking Content-Language: en-US To: qii.wang@mediatek.com Cc: matthias.bgg@gmail.com, linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org, wsa@kernel.org, nfraprado@collabora.com, kernel@collabora.com References: <20220411132107.136369-1-angelogioacchino.delregno@collabora.com> From: AngeloGioacchino Del Regno In-Reply-To: <20220411132107.136369-1-angelogioacchino.delregno@collabora.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Il 11/04/22 15:21, AngeloGioacchino Del Regno ha scritto: > 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 > Tested-by: Nícolas F. R. A. Prado Hello, this is a friendly ping to not let this be forgotten. Cheers, Angelo > --- > > v2: Fixed typos in commit description > > drivers/i2c/busses/i2c-mt65xx.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) >