Hi Devin, On Monday 01 March 2010 03:56:17 Devin Heitmueller wrote: > This might seem like a bit of a silly question, but I've been banging > my head on the wall for a while on this. > > I need to add a single private control to the saa7115 driver. > However, it's not clear to me exactly how this is supposed to work. > > The v4l2-ctl program will always use the extended controls interface > for private controls, since the code only uses the g_ctrl ioctl if the > class is V4L2_CTRL_CLASS_USER (and the control class for private > controls is V4L2_CID_PRIVATE_BASE). > > However, if you look at the actual code in v4l2-ioctl.c, the call for > g_ext_ctrls calls check_ext_ctrls(), which fails because > "V4L2_CID_PRIVATE_BASE cannot be used as control class when using > extended controls." > > The above two behaviors would seem to be conflicting. I don't think it should matter which API (the base one or the extended one) you use for controls, be they private, standard or whatever. I don't see a reason for disallowing some controls to be used through one or the other API. > My original plan was to implement it as a non-extended control, but > the v4l2-ctl application always sent the get call using the extended > interface. So then I went to convert saa7115 to use the extended > control interface, but then found out that the v4l2 core wouldn't > allow an extended control to use a private control number. > > To make matters worse, the G_CTRL function that supposedly passes > through calls to vidioc_g_ext_ctrl also calls check_ext_ctrl(), so if > you want to have a private control then you would need to implement > both the extended controls interface and the older g_ctrl in the > driver (presumably the idea was that you would be able to only need to > implement an extended controls interface, but that doesn't work given > the above). > > I can change v4l2-ctl to use g_ctrl for private controls if we think > that is the correct approach. But I didn't want to do that until I > knew for sure that it is correct that you can never have a private > extended control. Do we have extended *controls* ? All I see today is two APIs to access controls, a base *control API* and an extended *control API*. G_CTRL/S_CTRL should always be available to userspace. If you want to set a single control, the extended API isn't required. -- Regards, Laurent Pinchart -- 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
