Hi Hans,
On 1/28/19 5:03 AM, Hans Verkuil wrote:
Hi Shuah,
On 1/24/19 9:32 PM, Shuah Khan wrote:
Media Device Allocator API to allows multiple drivers share a media device.
This API solves a very common use-case for media devices where one physical
device (an USB stick) provides both audio and video. When such media device
exposes a standard USB Audio class, a proprietary Video class, two or more
independent drivers will share a single physical USB bridge. In such cases,
it is necessary to coordinate access to the shared resource.
Using this API, drivers can allocate a media device with the shared struct
device as the key. Once the media device is allocated by a driver, other
drivers can get a reference to it. The media device is released when all
the references are released.
- This patch series is tested on 5.0-rc3 and addresses comments on
v9 series from Hans Verkuil.
- v9 was tested on 4.20-rc6.
- Tested sharing resources with kaffeine, vlc, xawtv, tvtime, and
arecord. When analog is streaming, digital and audio user-space
applications detect that the tuner is busy and exit. When digital
is streaming, analog and audio applications detect that the tuner is
busy and exit. When arecord is owns the tuner, digital and analog
detect that the tuner is busy and exit.
I've been doing some testing with my au0828, and I am confused about one
thing, probably because it has been too long ago since I last looked into
this in detail:
Great.
Why can't I change the tuner frequency if arecord (and only arecord) is
streaming audio? If arecord is streaming, then it is recording the audio
from the analog TV tuner, right? So changing the analog TV frequency
should be fine.
Changing analog TV frequency would be s_frequency. The way it works is
any s_* calls would require holding the pipeline. In Analog TV case, it
would mean holding both audio and video pipelines for any changes
including TV.
As I recall, we discussed this design and the decision was to make all
s_* calls interfaces to hold the tuner. A special exception is g_tuner
in case of au0828. au0828 initializes the tuner from s_* interfaces and
its g_tuner interfaces. Allowing s_frequency to proceed will disrupt the
arecord audio stream.
Query (q_*) works just fine without holding the pipeline. I limited the
analog holds to just the ones that are required. The current set is
required to avoid audio stream disruptions.
I made sure v4l-ctl --all works when the pipeline is locked by any one
of the 3 (audio, video, DVB).
Hope this helps.
thanks,
-- Shuah
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