Hello Sakari, thank you for your reply (and finding a nice subject for this)! > On Mon, Jul 21, 2014 at 02:35:39PM +0200, Peter Meerwald wrote: > > how can I query the supported pixel format(s) of a sensor connected via > > media-ctl and exposed via /dev/videoX > > > > there is > > VIDIOC_ENUM_FMT (which fails) > > and > > VIDIOC_SUBDEV_ENUM_MBUS_CODE (which works, but on a subdev, not on > > /dev/videoX) > > > > v4l2_subdev_video_ops has .enum_mbus_fmt (this is SoC camera stuff?) > > > > v4l2_subdev_pad_ops has .enum_mbus_code > > > > > > the application just sees /dev/videoX and cannot do VIDIOC_ENUM_FMT > > what is the logic behind this? > > shouldn't a compabatibility layer be added turning VIDIOC_ENUM_FMT into > > VIDIOC_SUBDEV_ENUM_MBUS_CODE? > > The issue has been that enumerating should not change the state of the > device. Within a single device node things are fine, but in this case the > media bus pixel code at the other end of the link affects the result of the > enumeration. good to know this has been considered before > There hasn't been really a solution for this in the past; what has been > discussed as possible options have been (at least to my recollection) but > none has been implemented: > > 1) Use the media bux pixel code from the other end of the link. As there is > no common file handle to share the state with, the link configuration and > setting the media bus pixel code are necessary state changes before the > enumeration can take place, and the two must not be changed during the it. > This breaks the separation between configuration and enumeration. (There has > been a patch to the omap3isp driver which essentially did this long time ago > AFAIR.) > > 2) Use a reserved field in struct v4l2_fmtdesc to tell the pixel code. This > way enumeration can stay separate from configuration and is probably easier > for the user space as well. I vote for this: it's clean, simple and gets the > job done. I not sure if I fully understand your suggestion let's assume the following setup: sensor (subdev8) <-> OMAP3 CCDC (subdev2) <-> output (video2) userspace would query VIDIOC_ENUM_FMT on video2; what is the expected answer? and how would it be obtained? for me it would be good enough if first configuration via media-ctl is done, and ENUM_FMT video2 would just return at least one FMT that can be set so configuration would be fixed, I'm not interested in all possible FMTs regards, p. -- Peter Meerwald +43-664-2444418 (mobile) -- 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
