From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from lists.s-osg.org ([54.187.51.154]:52843 "EHLO lists.s-osg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752304AbbGNPDC (ORCPT ); Tue, 14 Jul 2015 11:03:02 -0400 Message-ID: <55A524A4.8090905@osg.samsung.com> Date: Tue, 14 Jul 2015 09:03:00 -0600 From: Shuah Khan MIME-Version: 1.0 To: Sakari Ailus , "Mauro Carvalho Chehab (m.chehab@samsung.com)" , Laurent Pinchart , Hans Verkuil CC: Linux Media Mailing List , Shuah Khan Subject: Re: Media Controller - graph_mutex References: <55A432D1.9060008@osg.samsung.com> <55A51763.8010506@linux.intel.com> In-Reply-To: <55A51763.8010506@linux.intel.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-media-owner@vger.kernel.org List-ID: On 07/14/2015 08:06 AM, Sakari Ailus wrote: > Hi Shuah, > > Shuah Khan wrote: >> All, >> >> ALSA has to make media_entity_pipeline_start() call in irq >> path. I am seeing warnings that the graph_mutex is unsafe irq >> lock as expected. We have to update MC start/stop pipeline >> to be irq safe for ALSA. Maybe there are other MC interfaces >> that need to be irq safe, but I haven't seen any problems with >> my limited testing. >> >> So as per options, graph_mutex could be changed to a spinlock. >> It looks like drivers hold this lock and it isn't abstracted to >> MC API. Unfortunate, this would require changes to drivers that >> directly hold the lock for graph walks if this mutex is changed >> to spinlock. >> >> e.g: drivers/media/platform/exynos4-is/fimc-isp-video.c >> >> Changes aren't complex, just that the scope isn't limited >> to MC API. >> >> Other ideas?? > > Do you have (preliminary?) patches and / or more information? I'd like > to understand why would ALSA need this. > > The graph_mutex is currently also taken when the link state is modified, > and the callbacks to the drivers may involve power state changes and > device initialisation. On some busses such as I2C these are blocking > operations. > I am getting close to sending the RFC patches for review. I am looking at one last issue in addition to this mutex problem. I have dmesg logs to send and I will send them when I send the patches, so you have code to look at as well as the dmesg. thanks, -- Shuah -- Shuah Khan Sr. Linux Kernel Developer Open Source Innovation Group Samsung Research America (Silicon Valley) shuahkh@osg.samsung.com | (970) 217-8978