Em Wed, 9 Aug 2017 11:03:40 +0300 Sakari Ailus <sakari.ailus@xxxxxx> escreveu: > Hi Mauro, > > Add stream control documentation. > > We have recently added support for hardware that makes it possible to have > pipelines that are controlled by more than two drivers. This necessitates > documenting V4L2 stream control behaviour for such pipelines. Perhaps I missed this one, but I'm not seeing any e-mail with "docs-rst: media: Document s_stream() video op usage" Please always submit patches via e-mail too, as it makes easier for us to comment/review when needed. In any case, I'm appending the patch contents here. I'll reply to it on a next e-mail. > From ef8e5d20b45b05290c56450d2130a0dc3c021c5a Mon Sep 17 00:00:00 2001 > From: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> > Date: Thu, 9 Mar 2017 15:07:57 +0200 > Subject: docs-rst: media: Document s_stream() video op usage > MIME-Version: 1.0 > Content-Type: text/plain; charset=UTF-8 > Content-Transfer-Encoding: 8bit > Cc: Linux Media Mailing List <linux-media@xxxxxxxxxxxxxxx>, > Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxx> > > As we begin to add support for systems with media pipelines controlled by > more than one device driver, it is essential that we precisely define the > responsibilities of each component in the stream control and common > practices. > > Specifically, this patch documents two things: > > 1) streaming control is done per sub-device and sub-device drivers > themselves are responsible for streaming setup in upstream sub-devices and > > 2) broken frames should be tolerated at streaming stop. It is the > responsibility of the sub-device driver to stop the transmitter after > itself if it cannot handle broken frames (and it should be probably be > done anyway). > > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx> > Acked-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx> > --- > Documentation/media/kapi/v4l2-subdev.rst | 36 ++++++++++++++++++++++++++++++++ > 1 file changed, 36 insertions(+) > > diff --git a/Documentation/media/kapi/v4l2-subdev.rst b/Documentation/media/kapi/v4l2-subdev.rst > index e1f0b726e438..100ffc783f72 100644 > --- a/Documentation/media/kapi/v4l2-subdev.rst > +++ b/Documentation/media/kapi/v4l2-subdev.rst > @@ -262,6 +262,42 @@ is called. After all subdevices have been located the .complete() callback is > called. When a subdevice is removed from the system the .unbind() method is > called. All three callbacks are optional. > > +Streaming control > +^^^^^^^^^^^^^^^^^ > + > +Starting and stopping the stream are somewhat complex operations that > +often require walking the media graph to enable streaming on > +sub-devices which the pipeline consists of. This involves interaction > +between multiple drivers, sometimes more than two. > + > +The ``.s_stream()`` op in :c:type:`v4l2_subdev_video_ops` is responsible > +for starting and stopping the stream on the sub-device it is called on. > +Additionally, if there are sub-devices further up in the pipeline, i.e. > +connected to that sub-device's sink pads through enabled links, the > +sub-device driver must call the ``.s_stream()`` video op of all such > +sub-devices. The sub-device driver is thus in control of whether the > +upstream sub-devices start (or stop) streaming before or after the > +sub-device itself is set up for streaming. > + > +.. note:: > + > + As the ``.s_stream()`` callback is called recursively through the > + sub-devices along the pipeline, it is important to keep the > + recursion as short as possible. To this end, drivers are encouraged > + not to internally call ``.s_stream()`` recursively in order to make > + only a single additional recursion per driver in the pipeline. This > + greatly reduces stack usage. > + > +Stopping the transmitter > +^^^^^^^^^^^^^^^^^^^^^^^^ > + > +A transmitter stops sending the stream of images as a result of > +calling the ``.s_stream()`` callback. Some transmitters may stop the > +stream at a frame boundary whereas others stop immediately, > +effectively leaving the current frame unfinished. The receiver driver > +should not make assumptions either way, but function properly in both > +cases. > + > V4L2 sub-device userspace API > ----------------------------- > > -- > 2.13.3 > Thanks, Mauro
