From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 66050919 for ; Mon, 1 Aug 2016 13:55:38 +0000 (UTC) Received: from s-opensource.com (ec2-52-27-115-49.us-west-2.compute.amazonaws.com [52.27.115.49]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id 05EE313B for ; Mon, 1 Aug 2016 13:55:37 +0000 (UTC) Date: Mon, 1 Aug 2016 10:55:31 -0300 From: Mauro Carvalho Chehab To: Lars-Peter Clausen Message-ID: <20160801105531.2687069a@recife.lan> In-Reply-To: References: <98eb563b-5d62-74df-692a-f2aa4f7b07b8@xs4all.nl> <20160729111303.GA10376@sirena.org.uk> <2525670.QGOuaEkzC4@avalon> <93f7ce34-c2e9-583f-2e6f-1f23ae76a761@xs4all.nl> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: ksummit-discuss@lists.linuxfoundation.org, "vegard.nossum@gmail.com" , "rafael.j.wysocki" , Valentin Rothberg , Marek Szyprowski Subject: Re: [Ksummit-discuss] [TECH TOPIC] Addressing complex dependencies and semantics (v2) List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Em Mon, 1 Aug 2016 15:33:22 +0200 Lars-Peter Clausen escreveu: > On 08/01/2016 03:21 PM, Hans Verkuil wrote: > > > > > > On 08/01/2016 03:09 PM, Laurent Pinchart wrote: > >> On Friday 29 Jul 2016 12:13:03 Mark Brown wrote: > >>> On Fri, Jul 29, 2016 at 09:45:55AM +0200, Hans Verkuil wrote: > >>>> My main problem is not so much with deferred probe (esp. for cyclic > >>>> dependencies it is a simple method of solving this, and simple is good). > >>>> My main problem is that you can't tell the system that driver A needs to > >>>> be probed after drivers B, C and D are probed first. > >>>> > >>>> That would allow us to get rid of v4l2-async.c which is a horrible hack. > >>>> > >>>> That code allows a bridge driver to wait until all dependent drivers are > >>>> probed. This really should be core functionality. > >>>> > >>>> Do other subsystems do something similar like > >>>> drivers/media/v4l2-core/v4l2-async.c? Does anyone know? > >>> > >>> ASoC does, it has an explicit card driver to join things together and > >>> that just defers probe until everything it needs is present. This was > >>> originally open coded in ASoC but once deferred probe was implemented we > >>> converted to that. > >> > >> Asynchronous bindings of components, as done in ASoC, DRM and V4L2, is a > >> problem largely solved (or rather hacked around), but I'm curious to know how > >> ASoC handles device unbinding (due to device removal or manual unbinding > >> through sysfs). With asynchronous binding we can more or less easily wait for > >> all components to be present before creating circular dependencies, but > >> breaking them to implement unbinding is an unsolved problem at least in V4L2. > >> > > > > We need to prevent subdevice drivers from being unbound. It's easy enough to > > do that (set suppress_bind_attrs to true), we just never did that. It's been > > on my TODO list for ages to make a patch adding that flag... > > > > You can only unbind bridge drivers. Unbinding subdevs is pointless in general > > and should be prohibited. Perhaps in the future with dynamically reconfigurable > > video pipelines (FPGA) you want that, but then you need to do a lot of > > additional work. For everything we have today we should just set > > suppress_bind_attrs to true. > > suppress_bind_attrs is the lazy solution and as you pointed out does not > work too well for all cases. Agreed. What we really need is a kind of "usage count" behavior to suppress unbinds, e. g. a device driver can be unbound only if any other driver using resources on it gets unbind first. That will solve most of unbind issues at the media subsystem. -- Thanks, Mauro