Hi Sakari, On Thu, Apr 30, 2020 at 05:15:52PM +0300, Sakari Ailus wrote: > On Thu, Apr 30, 2020 at 04:59:04PM +0300, Laurent Pinchart wrote: > > On Thu, Apr 30, 2020 at 04:31:25PM +0300, Sakari Ailus wrote: > > > On Thu, Apr 30, 2020 at 02:10:14PM +0300, Laurent Pinchart wrote: > > > > On Thu, Apr 30, 2020 at 12:42:33PM +0300, Sakari Ailus wrote: > > > >> On Tue, Apr 14, 2020 at 10:01:49PM +0200, Daniel Gomez wrote: > > > >>> Add min and max structures to the v4l2-subdev callback in order to allow > > > >>> the subdev to return a range of valid frame intervals. > > > >>> > > > >>> This would operate similar to the struct v4l2_subdev_frame_size_enum and > > > >>> its max and min values for the width and the height. In this case, the > > > >>> possibility to return a frame interval range is added to the v4l2-subdev level > > > >>> whenever the v4l2 device operates in step-wise or continuous mode. > > > >> > > > >> The current API only allows providing a list of enumerated values. That is > > > >> limiting indeed, especially on register list based sensor drivers where > > > >> vertical blanking is configurable. > > > >> > > > >> I guess this could be extended to cover what V4L2, more or less. If we tell > > > >> it's a range, is it assumed to be contiguous? We don't have try operation > > > >> for the frame interval, but I guess set is good enough. The fraction is > > > >> probably best for TV standards but it's not what camera sensors natively > > > >> use. (But for a register list based driver, the established practice > > > >> remains to use frame interval.) > > > >> > > > >> I'm also wondering the effect on existing user space; if a driver gives a > > > >> range, how will the existing programs work with such a driver? > > > >> > > > >> I'd add an anonymous union with the interval field, the other field being > > > >> min_interval. Then the current applications would get the minimum interval > > > >> and still continue to function. I guess compilers are modern enough these > > > >> days we can have an anonymous union in the uAPI? > > > > > > > > We can discuss all this, but given patch 3/3 in this series, I think > > > > this isn't the right API :-) The sensor driver should not expose the > > > > frame interval enumeration API. It should instead expose control of the > > > > frame rate through V4L2_CID_PIXEL_RATE, V4L2_CID_HBLANK and > > > > V4L2_CID_VBLANK. > > > > > > > > > > That would require also exposing the size of the pixel array (and the > > > analogue crop), in order to provide all the necessary information to > > > calculate the frame rate. No objections there; this is a new driver. > > > > > > There are however existing drivers that implement s_frame_interval subdev > > > ioctl; those might benefit from this one. Or would you implement the pixel > > > rate based control as well, and effectively deprecate the s_frame_interval > > > on those? > > > > That's what I would recommend, yes. I would only keep > > .s_frame_interval() for sensors that expose that concept at the hardware > > level (for instance with an integrated ISP whose firmware exposes a > > frame interval or frame rate control). > > Sounds good to me. > > Jacopo's set exposing read-only subdevs completes the puzzle so the user > space should have all it needs, right? Until we run into the next missing piece :-) -- Regards, Laurent Pinchart
