On Sun, 15 Mar 2009 08:14:56 -0700 (PDT) Trent Piepho <xyzzy@xxxxxxxxxxxxx> wrote: > > - this asks to have a kernel generated with CONFIG_NEW_LEDS, > > So? > > > - the user must use some new program to > > access /sys/class/leds/<device>, > > echo, cat? > > > - he must know how the LEDs of his webcam are named in the /sys > > tree. > > Just give them a name like video0:power and it will be easy enough to > associate them with the device. I think links in sysfs would do it > to, /sys/class/video4linux/video0/device/<ledname> or something like > that. > > The advantage of using the led class is that you get support for > triggers and automatic blink functions, etc. Sorry for I don't see the usage of blinking the LEDs for a webcam. Again, using the led class makes me wonder about: 1) The end users. Many Linux users don't know the kernel internal, nor which of the too many applications they should use to make their devices work. If no developper creates a tool to handle the webcams, the users have to search again and again. Even if there is a full documentation, they will try anything and eventually ask the kernel developpers why they cannot have their LEDs switched on. Actually, there are a few programs that can handle the webcam parameters. In fact I know only 'v4l2-ctl': I did not succeeded to compile qv4l2; v4l2ucp has been removed from Debian; and, anyway, these programs don't handle the VIDIOC_G_JPEGCOMP and VIDIOC_S_JPEGCOMP ioctls. 2) The memory overhead. Using the led class adds more kernel code and asks the webcam drivers to create a new device. Also, the function called for changing the LED brighness cannot sleep, so the use a workqueue is required. On contrary, with a webcam control, only one byte (for 8 LEDs) is added to the webcam structure and the change is immediatly done in the ioctl. 3) The development time. I already spent 2 hours to look how the led class was working. I am not sure to develop a full LED mechanism in less than 5 to 8 hours, and, as I cannot test it by myself, I will have to wait for testers to know if the various protections (USB access, USB disconnection) work in all cases. Otherwise, adding a new control in a driver may be done in less than half an hour, and, sure, it will work well at the first go! -- Ken ar c'hentañ | ** Breizh ha Linux atav! ** Jef | http://moinejf.free.fr/ -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
