[alsa-devel] [RFC/PATCH v6 03/12] media: Entities, pads and links

Laurent Pinchart laurent.pinchart at ideasonboard.com
Tue Dec 14 15:57:38 CET 2010

Hi Hans,

On Tuesday 14 December 2010 15:51:08 Hans Verkuil wrote:
> > Laurent Pinchart wrote:
> >> On Monday 13 December 2010 17:10:51 Clemens Ladisch wrote:
> >>> TYPE_EXT describes entities that represent some interface to the
> >>> external world, TYPE_INT those that are internal to the entire device.
> >>> (I'm not sure if that distinction is very useful, but TYPE_SUBDEV seems
> >>> to be an even more meaningless name.)
> >> 
> >> SUBDEV comes from the V4L2 world, and I agree that it might not be a
> >> very good
> >> name.
> >> 
> >> I'm not sure I would split entities in internal/external categories. I
> >> would
> >> create a category for connectors though.
> > 
> > I'm not disagreeing, but what is actually the distinction between types
> > and subtypes?  ;-)
> The type tells what the behavior is of an entity. E.g., type DEVNODE
> represents device node(s) in userspace, V4L2_SUBDEV represents a v4l2
> sub-device, etc. The subtype tells whether a V4L2_SUBDEV is a sensor or a
> receiver or whatever. Nice to know, but it doesn't change the way
> sub-devices work.
> In the case of connectors you would create a CONNECTOR type and have a
> bunch of subtypes for all the variations of connectors.
> That said, I'm not sure whether the distinction is useful for DEVNODEs.
> You do need to know the subtype in order to interpret the union correctly.
> Laurent, does the MC code test against the DEVNODE type? I.e., does the MC
> code ignore the subtype of a DEVNODE, or does it always use it?

The MC code uses the DEVNODE type, ignoring the subtype, for power management. 
When a device node is opened all entities in the chain need to be powered up.


Laurent Pinchart

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