Hi Hans, On Monday 07 January 2013 13:10:54 Hans Verkuil wrote: > On Mon January 7 2013 11:46:38 Andrzej Hajda wrote: > > Hi, > > > > I have included this proposition already in the post "[PATCH RFC 0/2] > > V4L: Add auto focus area control and selection" but it left unanswered. > > I repost it again in a separate e-mail, I hope this way it will be > > easier to attract attention. > > > > Problem description > > > > Currently V4L2 controls can have only single value (of type int, int64, > > string). Some hardware controls require more than single int parameter, > > for example to set auto-focus (AF) rectangle four coordinates should be > > passed, to set auto-focus spot two coordinates should be passed. > > > > Current solution > > > > In case of AF rectangle we can reuse selection API as in "[PATCH RFC > > 0/2] V4L: Add auto focus area control and selection" post. > > Pros: > > - reuse existing API, > > Cons: > > - two IOCTL's to perform one action, > > - non-atomic operation, Is it really an issue in your use cases, or is this only a theoretical problem ? > > - fits well only for rectangles and spots (but with unused fields width, > > height), in case of other parameters we should find a different way. > > > > Proposed solution > > > > The solution takes an advantage of the fact VIDIOC_(G/S/TRY)_EXT_CTRLS > > ioctls can be called with multiple controls per call. > > > > I will present it using AF area control example. > > > > There could be added four pseudo-controls, lets call them for short: > > LEFT, TOP, WIDTH, HEIGHT. > > Those controls could be passed together with > > V4L2_AUTO_FOCUS_AREA_RECTANGLE > > control in one ioctl as a kind of parameters. > > > > For example setting auto-focus spot would require calling > > VIDIOC_S_EXT_CTRLS with the following controls: > > - V4L2_CID_AUTO_FOCUS_AREA = V4L2_AUTO_FOCUS_AREA_RECTANGLE > > - LEFT = ... > > - RIGHT = ... > > > > Setting AF rectangle: > > - V4L2_CID_AUTO_FOCUS_AREA = V4L2_AUTO_FOCUS_AREA_RECTANGLE > > - LEFT = ... > > - TOP = ... > > - WIDTH = ... > > - HEIGHT = ... > > > > Setting AF object detection (no parameters required): > > - V4L2_CID_AUTO_FOCUS_AREA = V4L2_AUTO_FOCUS_AREA_OBJECT_DETECTION > > If you want to do this, then you have to make LEFT/TOP/WIDTH/HEIGHT real > controls. There is no such thing as a pseudo control. So you need five > new controls in total: > > V4L2_CID_AUTO_FOCUS_AREA > V4L2_CID_AUTO_FOCUS_LEFT > V4L2_CID_AUTO_FOCUS_RIGHT > V4L2_CID_AUTO_FOCUS_WIDTH > V4L2_CID_AUTO_FOCUS_HEIGHT > > I have no problem with this from the point of view of the control API, but > whether this is the best solution for implementing auto-focus is a different > issue and input from sensor specialists is needed as well (added Laurent > and Sakari to the CC list). > > The primary concern I have is that this does not scale to multiple focus > rectangles. This might not be relevant to auto focus, though. Time to implement a rectangle control type ? Or to make it possible to issue atomic transactions across ioctls ? We've been postponing this discussion for ages. > > I have presented all three cases to show the advantages of this solution: > > - atomicity - control and its parameters are passed in one call, > > - flexibility - we are not limited by a fixed number of parameters, > > - no-redundancy - we can pass only required parameters > > > > (no need to pass null width and height in case of spot selection), > > > > - extensibility - it is possible to extend parameters in the future, > > for example add parameters to V4L2_AUTO_FOCUS_AREA_OBJECT_DETECTION, > > without breaking API, > > - backward compatibility, > > - re-usability - this schema could be used in other controls, > > > > pseudo-controls could be re-used in other controls as well. > > > > - API backward compatibility. -- 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
