From mboxrd@z Thu Jan 1 00:00:00 1970 From: Valentin Longchamp Date: Thu, 28 Jan 2010 14:02:54 +0000 Subject: Re: [Q] udev and soc-camera Message-Id: <4B61990E.5010604@epfl.ch> List-Id: References: <4B60CB5A.7000109@epfl.ch> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Kay Sievers Cc: "linux-media@vger.kernel.org" , "linux-hotplug@vger.kernel.org" Kay Sievers wrote: > On Thu, Jan 28, 2010 at 00:25, Valentin Longchamp > wrote: >> I have a system that is built with OpenEmbedded where I use a mt9t031 camera >> with the soc-camera framework. The mt9t031 works ok with the current kernel >> and system. >> >> However, udev does not create the /dev/video0 device node. I have to create >> it manually with mknod and then it works well. If I unbind the device on the >> soc-camera bus (and then eventually rebind it), udev then creates the node >> correctly. This looks like a "timing" issue at "coldstart". >> >> OpenEmbedded currently builds udev 141 and I am using kernel 2.6.33-rc5 (but >> this was already like that with earlier kernels). >> >> Is this problem something known or has at least someone already experienced >> that problem ? > > You need to run "udevadm trigger" as the bootstrap/coldplug step, > after you stared udev. All the devices which are already there at that > time, will not get created by udev, only new ones which udev will see > events for. The trigger will tell the kernel to send all events again. > > Or just use the kernel's devtmpfs, and all this should work, even > without udev, if you do not have any other needs than plain device > nodes. > Thanks a lot Kay, you pointed me exactly where I needed to watch. OpenEmbedded adds udevadm trigger a big list of --susbsystem-nomatch options as soon as you are not doing your first boot anymore and video4linux is among them. I either have to remove this option in the script or understand why my other /dev nodes are kept (ttys are doing fine with the same treatment for instance) and not video4linux ones (it looks like they are using DEVCACHE or something like this). But I would prefer the first alternative since cameras may be unplugged on some robots. Val -- Valentin Longchamp, PhD Student, EPFL-STI-LSRO1 valentin.longchamp@epfl.ch, Phone: +41216937827 http://people.epfl.ch/valentin.longchamp MEB3494, Station 9, CH-1015 Lausanne