Hi Hans, On Mon, Dec 07, 2020 at 02:16:39PM +0100, Hans Verkuil wrote: > On 07/12/2020 13:46, Sakari Ailus wrote: > > Hi Hans, > > > > Thanks for the patch. > > > > On Mon, Dec 07, 2020 at 12:18:55PM +0100, Hans Verkuil wrote: > >> This driver does not support composition, only cropping. > >> Composition means that the sensor can output e.g. 1920x1080, > >> but can compose a cropped 1280x720 image in the middle of the > >> 1920x1080 canvas, filling in the unused area with a background > >> color. > > > > That's how this would work on V4L2 video nodes... > > > >> > >> That's not supported at all. So drop the bogus composition support. > > > > But this is a sub-device driver. On sub-devices the COMPOSE target is used > > for configuring scaling, binning and sub-sampling. I don't know about the > > capabilities of this particular driver but the code > > (__imx274_change_compose function in particular) looks very much such that > > it does support binning. > > > > That should be done via set_fmt. There you select the output width and height. > > So if set_fmt sets 1920x1080, and the crop is 960x540, then you scale (or > do binning/sub-sampling). Compose means composing the image into a larger > canvas. For this driver the compose rectangle is always equal to the > format, so set_selection(COMPOSE) is identical to set_fmt(). > > If it was real composition, then there would have to be a try_compose as > well, just as there is a try_crop. Instead set_selection(COMPOSE) fills in On sub-devices there's a try context that's file handle specific. > try_fmt. Clearly wrong. Not more than using set_fmt if you look at the documentation: <URL:https://hverkuil.home.xs4all.nl/spec/userspace-api/v4l/dev-subdev.html#order-of-configuration-and-format-propagation> In this case it's just on the sink pad, as the sub-device exports no source pads. I think there are probably a few such drivers around. Which sub-device drivers configure scaling based on set_fmt? I'm only aware of omap3isp which pre-dates the selection API. -- Kind regards, Sakari Ailus
