On Sat, 27 Feb 2010 08:53:16 +0100 Hans de Goede <hdego...@redhat.com> wrote:
> This is true for a lot of cameras, so if we are going to add a way to > support control of the LED separate of the streaming state, we > should do that at the gspca_main level, and let sub drivers which > support this export a set_led callback function. > > I must say I personally don't see much of a use case for this feature, > but I believe JF Moine does, so I'll leave further comments and > review of this to JF. I do believe it is important that if we go this > way we do so add the gspca_main level. Hi, I don't like this mechanism to switch on or off the webcam LEDs. Here are some arguments (some of them were sent last year to the list): 1) End users. Many Linux users don't know the kernel internals, nor which of the too many applications they should use to make their devices work. Actually, there are a few X11 programs in common Linux distros which can handle the webcam parameters: I just know about vlc and v4l2ucp, and they don't even handle the VIDIOC_G_JPEGCOMP and VIDIOC_S_JPEGCOMP ioctls which are part of the v4l2 API. The LED interface uses the /sys file system. Will the webcam programs offer access to this interface? I don't believe it. So, the users will have to search how they can switch on or off the LEDs of their webcams, and then, when found, they should start a X terminal and run a command to do the job! On the other hand, a webcam LED control, whether general or private, is available in the graphical interface as soon as the driver offers it. 2) 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) Development. If nobody wants a LED control in the v4l2 interface, I think the code added to access the led class could be splitted between the different subsystem. For example, the workqueue handling could be done in the led class itself... Cheers. -- 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
