On Sunday, January 23, 2011 16:15:03 Hans de Goede wrote: > Hi, > > On 01/22/2011 12:06 PM, Hans Verkuil wrote: > > It is a bit tricky to handle autogain/gain type scenerios correctly. Such > > controls need to be clustered and the V4L2_CTRL_FLAG_UPDATE should be set on > > the non-auto controls. If you set a non-auto control without setting the > > auto control at the same time, then the auto control should switch to manual > > mode. And usually the non-auto controls must be marked volatile, but this should > > only be in effect if the auto control is set to auto. > > > > The chances of drivers doing all these things correctly are pretty remote. > > So a new v4l2_ctrl_auto_cluster function was added that takes care of these > > issues. > > I like the concept of this, but I'm not so happy with the automatically put > the auto control in manual mode. We've discussed this before and iirc we > came to the conclusion then that the proper thing to do is to mark the > controls as read only, when the related auto control is in auto mode. > > This is what the UVC spec for example mandates and what the current UVC driver > does. Combining this with an app which honors the update and the read only > flag (try gtk-v4l), results in a nice experience. User enables auto exposure > -> exposure control gets grayed out, put exposure back manual -> control > is ungrayed. > > So this new auto_cluster behavior would be a behavioral change (for both the > uvc driver and several gspca drivers), and more over an unwanted one IMHO > setting one control should not change another as a side effect. Actually, I've been converting a whole list of subdev drivers recently (soc_camera, ov7670) and they all behaved like this. So I didn't change anything. There is nothing preventing other drivers from doing something different. That said, changing the behavior to your proposal may not be such a bad idea. But then I need the OK from all driver authors involved, since this would mean a change of behavior for them. The good news is that once they use the new framework function I only need to change what that function does and I don't need to change any of those drivers. So I will proceed for now by converting those drivers to use this new function, and at the same time I can contact the authors and ask what their opinion is of this change. I'm hoping for more feedback as well from what others think. BTW, if I understand the gspca code correctly then it seems that if an e.g. autogain control is set to 1, then the gain control effectively disappears. I think queryctrl will just never return it. That can't be right. I tried to test it but while my zc3xx-based webcam has autogain there is interestingly enough no corresponding manual gain control. Regards, Hans -- Hans Verkuil - video4linux developer - sponsored by Cisco -- 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
