Re: [PATCH v9 11/46] media: Documentation: Document S_ROUTING behaviour

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Hi Laurent,

On Tue, Apr 23, 2024 at 03:59:44PM +0300, Laurent Pinchart wrote:
> Hi Sakari,
> 
> On Tue, Apr 23, 2024 at 10:08:05AM +0000, Sakari Ailus wrote:
> > On Fri, Apr 19, 2024 at 08:17:20PM +0300, Laurent Pinchart wrote:
> > > On Tue, Apr 16, 2024 at 10:32:44PM +0300, Sakari Ailus wrote:
> > > > Document S_ROUTING behaviour for different devices.
> > > > 
> > > > Generally in devices that produce streams the streams are static and some
> > > > can be enabled and disabled, whereas in devices that just transport them
> > > > or write them to memory, more configurability is allowed. Document this.
> > > > 
> > > > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > > > Reviewed-by: Julien Massot <julien.massot@xxxxxxxxxxxxx>
> > > > ---
> > > >  .../userspace-api/media/v4l/dev-subdev.rst    | 24 +++++++++++++++++++
> > > >  1 file changed, 24 insertions(+)
> > > > 
> > > > diff --git a/Documentation/userspace-api/media/v4l/dev-subdev.rst b/Documentation/userspace-api/media/v4l/dev-subdev.rst
> > > > index d30dcb9e2537..de8dfd4f11a5 100644
> > > > --- a/Documentation/userspace-api/media/v4l/dev-subdev.rst
> > > > +++ b/Documentation/userspace-api/media/v4l/dev-subdev.rst
> > > > @@ -593,6 +593,30 @@ Any configurations of a stream within a pad, such as format or selections,
> > > >  are independent of similar configurations on other streams. This is
> > > >  subject to change in the future.
> > > >  
> > > > +Device types and routing setup
> > > > +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > > > +
> > > > +Different kinds of sub-devices have differing behaviour for route activation,
> > > > +depending on the hardware. In all cases, however, only routes that have the
> > > > +``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag set are active.
> > > > +
> > > > +Devices generating the streams may allow enabling and disabling some of the
> > > > +routes or the configuration is fixed. If the routes can be disabled, not
> > > 
> > > "... some of the routes, or have a fixed routing configuration."
> > 
> > Seems fine.
> > 
> > > > +declaring the routes (or declaring them without
> > > > +``VIDIOC_SUBDEV_STREAM_FL_ACTIVE`` flag set) in ``VIDIOC_SUBDEV_S_ROUTING`` will
> > > > +disable the routes while the sub-device driver retains the streams and their
> > > > +format and selection configuration.
> > > 
> > > I still find the "retains their format and selection configuration"
> > > quite unclear :-S
> > 
> > Alternatively we could say that the routes are simply not active, without
> > referring to explicitly to formats and selections. I.e.:
> > 
> > If the routes can be disabled, not declaring the routes (or declaring them
> > without ``VIDIOC_SUBDEV_STREAM_FL_ACTIVE`` flag set) in
> > ``VIDIOC_SUBDEV_S_ROUTING`` will disable the routes.
> 
> I'm fine with that.
> 
> > > > The ``VIDIOC_SUBDEV_S_ROUTING`` will still
> > > 
> > > s/will still/ioctl will still/
> > 
> > Both seem to exist, more common is without "ioctl":
> > 
> > $ git grep '[`<]VIDIOC_SUBDEV' -- Documentation/userspace-api/media/|wc -l
> > 84
> > $ git grep -i "VIDIOC_SUBDEV.*ioctl" -- Documentation/userspace-api/media/|wc -l
> > 34
> 
> You'll often find "ioctl" at the beginning of the next line :-) If you
> would like to avoid it, you should drop "The" at the beginning of the
> sentence.

Sounds good.

> 
> > > > +return such routes back to the user in the routes array, with the
> > > > +``V4L2_SUBDEV_STREAM_FL_ACTIVE`` flag unset.
> > > > +
> > > > +Devices transporting the streams almost always have more configurability with
> > > > +respect to routing. Typically any route between the sub-device's sink and source
> > > > +pads is possible, and multiple routes (usually up to certain limited number) may
> > > > +be active simultaneously. For such devices, no routes are created by the driver
> > > > +and user-created routes are fully replaced when ``VIDIOC_SUBDEV_S_ROUTING`` is
> > > > +called on the sub-device. Such newly created routes have the device's default
> > > > +configuration for format and selection rectangles.
> > > > +
> > > >  Configuring streams
> > > >  ^^^^^^^^^^^^^^^^^^^
> > > >  
> 

-- 
Regards,

Sakari Ailus




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