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 C1F0FC5479D for ; Mon, 9 Jan 2023 05:46:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234160AbjAIFqe (ORCPT ); Mon, 9 Jan 2023 00:46:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34250 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234414AbjAIFqY (ORCPT ); Mon, 9 Jan 2023 00:46:24 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C3D7BFF5 for ; Sun, 8 Jan 2023 21:46:21 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 725A0B80CB8 for ; Mon, 9 Jan 2023 05:46:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 13236C433D2; Mon, 9 Jan 2023 05:46:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1673243179; bh=oWKT64cyNa8ErN5yILzdB7muatJ9WA8Jd9QKW9SzBYU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=QPCTin5pOx2rnZdmgjmIrxLo797O7HjbLDhuuFH+vF/1gDjpoldinTIDL9U4hjMXJ 58jPJxwOf4NwGqkHLZhRmot53mGx+JQX8Lb6ppb50cGsX0aHLY8Lz3xKWT4kHBoN5n d4VP+zUTzIk1v6vpS/L3IByvdHItYJTw+WhbJk3hN5mTzOk7vGON+sFk8dDaeH2VKd r6NYt5vra6/rNffsmlYHkm/pfF5u3eP9fKrjYT8CiAvOY4hoAHJon9DOgMZpoEx9Yg HIsCPgEJ7/nYqUitS2wtTCiYs6CWL7f7dtuKNtBiVqRb50dpFSIAQp1afZGM6yeCiI DA354fAlTab/A== Date: Mon, 9 Jan 2023 13:46:15 +0800 From: Tzung-Bi Shih To: Chen-Yu Tsai Cc: Benson Leung , Guenter Roeck , AngeloGioacchino Del Regno , chrome-platform@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH] platform/chromeos: cros_ec: Use per-device lockdep key Message-ID: References: <20230106045537.1243887-1-wenst@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 07, 2023 at 01:43:57PM +0800, Chen-Yu Tsai wrote: > On Fri, Jan 6, 2023 at 5:08 PM Tzung-Bi Shih wrote: > > > > On Fri, Jan 06, 2023 at 12:55:37PM +0800, Chen-Yu Tsai wrote: > > > Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to > > > the following lock sequences: > > > > > > 1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock) > > > 2. lock(&ec_dev->lock); lock(prepare_lock); > > > > > > The actual dependency chains are much longer. The shortened version > > > looks somewhat like: > > > > > > 1. cros-ec-rpmsg on mtk-scp > > > ec_dev->lock -> prepare_lock > > > 2. In rt5682_i2c_probe() on native I2C bus: > > > prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock > > > 3. In rt5682_i2c_probe() on native I2C bus: > > > regmap->lock -> i2c_adapter->bus_lock > > > 4. In sbs_probe() on cros-ec-i2c (passthrough) I2C bus on cros-ec > > > i2c_adapter->bus_lock -> ec_dev->lock > > > > > > While lockdep is correct that the shared lockdep classes have a circular > > > dependency, it is bogus because > > > > > > a) 2+3 happen on a native I2C bus > > > b) 4 happens on the actual EC on ChromeOS devices > > > c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just > > > happen to expose a cros-ec interface, but do not have a passthrough > > > I2C bus > > > > > > In short, the "dependencies" are actually on different devices. > > > > Path of 4 looks weird to me. > > > > Could you point out where sbs_probe() gets to acquire ec_dev->lock? > > sbs_probe() calls sbs_get_battery_presence_and_health(), which > > -> does an I2C transfer. This SBS instance is connected on the I2C bus > on the EC, so the I2C transfer > > -> acquires i2c_adapter->bus_lock, and I see. Another question: the i2c_adapter here should be different from the native I2C bus in 2 and 3. Did they really form the circular dependencies?