Hi Sakari, On Thu, Apr 30, 2020 at 05:18:49PM +0300, Sakari Ailus wrote: > On Thu, Apr 30, 2020 at 05:17:53PM +0300, Laurent Pinchart wrote: > > 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 :-) > > I was thinking of the frame rate configuration. Can you confirm that? I believe so, yes. -- Regards, Laurent Pinchart
