From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guennadi Liakhovetski Subject: Re: [ANN] Meeting minutes of the Cambourne meeting Date: Tue, 30 Aug 2011 00:38:12 +0200 (CEST) Message-ID: References: <201107261647.19235.laurent.pinchart@ideasonboard.com> <201108291508.59649.laurent.pinchart@ideasonboard.com> <201108300026.05489.laurent.pinchart@ideasonboard.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <201108300026.05489.laurent.pinchart-ryLnwIuWjnjg/C1BVhZhaw@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Sender: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org To: Laurent Pinchart Cc: Tomasz Stanislawski , Hans Verkuil , Sakari Ailus , Mauro Carvalho Chehab , devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org, Sylwester Nawrocki , Tuukka Toivonen , Sylwester Nawrocki , Marek Szyprowski , linux-media List-Id: devicetree@vger.kernel.org On Tue, 30 Aug 2011, Laurent Pinchart wrote: > Hi Guennadi, > > On Tuesday 30 August 2011 00:20:09 Guennadi Liakhovetski wrote: > > On Mon, 29 Aug 2011, Laurent Pinchart wrote: > > > > [snip] > > > > > My idea was to let the kernel register all devices based on the DT or > > > board code. When the V4L2 host/bridge driver gets registered, it will > > > then call a V4L2 core function with a list of subdevs it needs. The V4L2 > > > core would store that information and react to bus notifier events to > > > notify the V4L2 host/bridge driver when all subdevs are present. At that > > > point the host/bridge driver will get hold of all the subdevs and call > > > (probably through the V4L2 core) their .registered operation. That's > > > where the subdevs will get access to their clock using clk_get(). > > > > Correct me, if I'm wrong, but this seems to be the case of sensor (and > > other i2c-client) drivers having to succeed their probe() methods without > > being able to actually access the hardware? > > That's right. I'd love to find a better way :-) Note that this is already the > case for many subdev drivers that probe the hardware in the .registered() > operation instead of the probe() method. Then why do you think it is better, than adding devices from bridge drivers? Think about hotpluggable devices - drivers create devices all the time - USB etc. Why cannot we do the same? As a historic reference: soc-camera used to do this too before - probe without hardware access and "really-probe" after the host turns on the clock. Then we switched to registering devices later. I like the present approach better. Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/