From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx1.redhat.com ([209.132.183.28]:52250 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753289AbcCGTAy (ORCPT ); Mon, 7 Mar 2016 14:00:54 -0500 Subject: Re: [PATCH 0/2] [media] gspca_kinect: enable both video and depth streams To: Ulrik de Muelenaere , linux-media@vger.kernel.org References: Cc: Antonio Ospite From: Hans de Goede Message-ID: <56DDCFDE.8020209@redhat.com> Date: Mon, 7 Mar 2016 20:00:46 +0100 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: Hi Ulrik, On 06-03-16 14:50, Ulrik de Muelenaere wrote: > Hello, > > The Kinect produces both a video and depth stream, but the current implementation of the > gspca_kinect subdriver requires a depth_mode parameter at probe time to select one of > the streams which will be exposed as a v4l device. This patchset allows both streams to > be accessed as separate video nodes. > > A possible solution which has been discussed in the past is to call gspca_dev_probe() > multiple times in order to create multiple video nodes. See the following mails: > > http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/26194/focus=26213 > http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/76715/focus=78344 > > In the second mail linked above, it was mentioned that gspca_dev_probe() cannot be > called multiple times for the same USB interface, since gspca_dev_probe2() stores a > pointer to the new gspca_dev as the interface's private data. This is required for > gspca_disconnect(), gspca_suspend() and gspca_resume(). As far as I can tell, this is > the only reason gspca_dev_probe() cannot be called multiple times. > > The first patch fixes this by storing other devices linked to the same interface as a > linked list. The second patch then calls gspca_dev_probe() twice in the gspca_kinect > subdriver, to create a video node for each stream. > > Some notes on error handling, which I think should be reviewed: > > * I could not test the gspca_suspend() and gspca_resume() functions. From my evaluation > of the code, it seems that the only effect of returning an error code from > gspca_resume() is that a message is logged. Therefore I decided to attempt to resume > each gspca_dev when the interface is resumed, even if one fails. Bitwise OR seems > like the best way to combine potentially multiple error codes. > > * In the gspca_kinect subdriver, if the second call to gspca_dev_probe() fails, the > first video node will still be available. I handle this case by calling > gspca_disconnect(), which worked when I was testing, but I am not sure if this is the > correct way to handle it. Thanks for the patch-set overall I like it, one thing which worries is me is that sd_start_video and sd_start_depth may race, which is esp. problematic taking into account that both start/stop the depth stream (see the comment about this in sd_start_video()) this will require some coordination, so you like need to do something a bit more advanced and create a shared data struct somewhere for coordination (and with a lock in it). Likewise the v4l2 core is designed to have only one struct v4l2_device per struct device, so you need to modify probe2 to not call v4l2_device_register when it is called a second time for the same intf, and to make gspca_dev->vdev.v4l2_dev point to the v4l2_dev of the first gspca_dev registered. You will also need some changes for this in gspca_disconnect, as you will need to do all the calls on &gspca_dev->v4l2_dev only for the first registered device there, and you will need to do all the calls in gspca_release except for the v4l2_device_unregister() in a loop like you're using in disconnect. Note since you need a shared data struct anyways it might be easier to just use that (add some shared pointer to struct gspca_dev) for the array of gspca_devs rather then using the linked list, as for disconnect / release you will want to use the first registered gspca_dev to get the v4l2_dev address, and your linked approach gives you the last. Regards, Hans > > Regards, > Ulrik > > Ulrik de Muelenaere (2): > [media] gspca: allow multiple probes per USB interface > [media] gspca_kinect: enable both video and depth streams > > drivers/media/usb/gspca/gspca.c | 129 +++++++++++++++++++++++---------------- > drivers/media/usb/gspca/gspca.h | 1 + > drivers/media/usb/gspca/kinect.c | 28 +++++---- > 3 files changed, 91 insertions(+), 67 deletions(-) >