lkml.org 
[lkml]   [2010]   [Nov]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [RFC/PATCH v6 03/12] [alsa-devel] media: Entities, pads and links
    On Thu, Nov 25, 2010 at 04:21:38PM +0100, Laurent Pinchart wrote:
    > On Thursday 25 November 2010 10:38:05 Clemens Ladisch wrote:

    > > ALSA has PCM and MIDI devices, and several types of mixer controls.
    > > (It also has hardware dependent and timer devices, but I don't think
    > > these would need topology information.) So we need at least these:
    > > MEDIA_ENTITY_TYPE_NODE_ALSA_PCM
    > > MEDIA_ENTITY_TYPE_NODE_ALSA_MIDI
    > > MEDIA_ENTITY_TYPE_SUBDEV_ALSA_CONTROL

    > I agree about PCM and MIDI, but I'm not sure about controls. If controls are
    > part of an entity, the entity will be reported through the media controller
    > API. If information about that entity can be queried through existing APIs
    > (ALSA, V4L, ...) those APIs should be used. For instance, on the V4L side,
    > V4L2 sub-devices are mapped to entities and also have a device node which can
    > be used to enumerate the controls supported by the subdev. The media
    > controller only reports the entity -> major:minor mapping to let applications
    > find the device and query it directly.

    For audio we don't currently have a sensible API for associating
    controls with any sort of map of how the device is laid out, userspace
    has to play guessing games.

    > I think we will need a new ioctl in the media controller API to report
    > advanced information about an entity. This could be used to report controls
    > implemented by an ALSA element if ALSA doesn't provide a way to do that
    > directly. Another use case, which make me think that such an ioctl would be
    > needed, is to report UVC extension units type (16-byte GUID) to userspace.

    That seems reasonable.


    \
     
     \ /
      Last update: 2010-11-25 16:31    [W:3.528 / U:0.048 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site