Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754952AbdGTOYZ (ORCPT ); Thu, 20 Jul 2017 10:24:25 -0400 Received: from pandora.armlinux.org.uk ([78.32.30.218]:52056 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753834AbdGTOYY (ORCPT ); Thu, 20 Jul 2017 10:24:24 -0400 Date: Thu, 20 Jul 2017 15:24:13 +0100 From: Russell King - ARM Linux To: Liviu Dudau Cc: David Airlie , DRI devel , LKML Subject: Re: [PATCH] drm/i2c: tda998x: Fix lockdep warning about possible circular dependency Message-ID: <20170720142413.GB31807@n2100.armlinux.org.uk> References: <20170720110450.7435-1-Liviu.Dudau@arm.com> <20170720113853.GX31807@n2100.armlinux.org.uk> <20170720114449.GA19026@n2100.armlinux.org.uk> <20170720125404.GA3532@e110455-lin.cambridge.arm.com> <20170720130829.GY31807@n2100.armlinux.org.uk> <20170720141910.GC3532@e110455-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170720141910.GC3532@e110455-lin.cambridge.arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1554 Lines: 33 On Thu, Jul 20, 2017 at 03:19:10PM +0100, Liviu Dudau wrote: > On Thu, Jul 20, 2017 at 02:08:29PM +0100, Russell King - ARM Linux wrote: > > On Thu, Jul 20, 2017 at 01:54:04PM +0100, Liviu Dudau wrote: > > > On Thu, Jul 20, 2017 at 12:44:49PM +0100, Russell King - ARM Linux wrote: > > > > Actually, scrub that idea - drm_helper_probe_single_connector_modes() > > > > calls drm_edid_to_eld() for these cases anyway, so we must call > > > > drm_helper_probe_single_connector_modes() with the audio_mutex held. > > > > > > OK, so the lockdep warning is spurious? > > > > I don't think so. I think there's two ways to solve this: > > > > 1. replace the audio_mutex in tda998x_audio_get_eld() and > > tda998x_connector_fill_modes() with a new mutex (eld_mutex) to > > protect just the ELD. > > > > 2. remove the mutex from these two functions, and take the connection_mutex > > modeset lock in tda998x_audio_get_eld(). > > > > However, I don't have a view on which would be best. > > If you don't mind, I took the liberty of picking option 2, just because > I don't like adding new locks when existing ones might do the job. I don't mind - but one question for the DRM people in connection with your patch is whether we need the acquire context for this relatively simple lock/copy/unlock sequence. This path for getting the ELD shouldn't be holding any other DRM locks. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.