media / v4l2-mc: wishlist for complex cameras (was Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline)

[Philipp Zabel]

On Thu, 2017-03-16 at 10:47 +0100, Philippe De Muyter wrote:
> On Thu, Mar 16, 2017 at 10:26:00AM +0100, Philipp Zabel wrote:
> > On Wed, 2017-03-15 at 14:55 -0400, Nicolas Dufresne wrote:
> > > Le mercredi 15 mars 2017 à 11:50 +0100, Philippe De Muyter a écrit :
> > > > > I would say: camorama, xawtv3, zbar, google talk, skype. If it runs
> > > > > with those, it will likely run with any other application.
> > > > > 
> > > > 
> > > > I would like to add the 'v4l2src' plugin of gstreamer, and on the
> > > > imx6 its
> > > 
> > > While it would be nice if somehow you would get v4l2src to work (in
> > > some legacy/emulation mode through libv4l2),
> > 
> > v4l2src works just fine, provided the pipeline is configured manually in
> > advance via media-ctl.
> 
> Including choosing the framerate ?  Sorry, I have no time these days
> to test it myself.

No, the framerate is set with media-ctl on the CSI output pad. To really
choose the framerate, the element would indeed need a deeper
understanding of the pipeline, as the resulting framerate depends on at
least the source v4l2_subdevice (sensor) framerate and the CSI frame
skipping.

> And I cited imxv4l2videosrc for its ability to provide the physical address
> of the image buffers for further processing by other (not necessarily next
> in gstreamer pipeline, or for all frames) hardware-accelerated plugins likes
> the h.264 video encoder.  As I am stuck with fsl/nxp kernel and driver on that
> matter, I don't know how the interfaces have evolved in current linux kernels.

The physical address of the image buffers is hidden from userspace by
dma-buf objects, but those can be passed around to the next driver
without copying the image data.

regards
Philipp