Hi Vinay,
On Monday 19 December 2011 21:08:31 vkalia@xxxxxxxxxxxxxx wrote:
>
> I am trying to implement a video encoder v4l2 device and need your help to
> find answers to some of the questions. There is one hardware core which can
> do multiple sessions (multiple file handles) of encode simultaneously. The
> encode functionalty needs to be exposed to userspace as well as kernel
> through standard set of APIs. Userspace should be able to use this
> functionality through V4l2 interface and another kernel module should be
> able to use encoder as a subdevice. I am trying to explore the framework to
> achieve this and have following questions:
>
> 1. I am planning to create a V4L2 device and also initializing it as a
> subdev in the probe function i.e the probe function of this driver will
> have:
> struct venc_device {
> struct v4l2_device v4l2_dev;
> struct v4l2_subdev sd;
> };
>
> struct venc_device *vdev;
> v4l2_device_register(&vdev->v4l2_dev);
> v4l2_subdev_init(&vdev->sd, venc_sd_ops);
>
> How do other modules discover this subdevice. Is there an API I can use
> to find module by name?
>
> 2. Most of the subdevice interface functions have input parameters as
> "struct v4l2_subdev *sd" and another API specific structure. How do I
> distinguish between different instances (file handles) of a subdevice.
The short answer is that you don't.
If your hardware block can encode a fixed number of streams separately, one
possible solution would be to create N subdevices, or to create a single
subdevice with N input pads and N output pads, where N is the number of
logical streams. Input and output pads could then be connected to video nodes
or to other subdevices in the system.
Another solution is to use the mem-to-mem framework, which allows streams
multiplexing through multiple opens. However, there is no clear mapping to
subdevs (that I'm aware of) at the moment.
Can you share a bit more information about your hardware ? A block diagram
would be useful.
> Do I always need to pass file handle/instance specific information in
> "void *arg" of the ioctl subdev core ops.
>
> 3. Controls are instance specific, eg: one encoder application might encode
> at bitrate of 4Mbps and another at 128kbps, so I want controls to be
> specific to file handles. I see that the control handler has been moved
> to v4l2_fh structure for this purpose. How do I do it for subdevices so
> that the v4l2 device using this subdevice inherits the instance specific
> controls defined by the subdevice.
--
Regards,
Laurent Pinchart
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