Re: [PATCH v10 0/4] Media Device Allocator API
From: shuah
Date: Thu Jan 31 2019 - 19:46:28 EST
Hi Hans,
On 1/30/19 12:42 AM, Hans Verkuil wrote:
On 1/30/19 2:50 AM, shuah wrote:
On 1/29/19 2:43 AM, Hans Verkuil wrote:
On 1/29/19 12:48 AM, shuah wrote:
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.
So I am not sure about that ('avoid audio stream disruptions'): if I
stream video AND use arecord, then I can just set the frequency while
streaming. Doesn't that interrupt audio as well? And are you sure changing
the tuner frequency actually disrupts audio? And if audio is disrupted,
are we talking about a glitch or is audio permanently disrupted?
I think it is a glitch. I will run some tests and let you know.
That's basically the inconsistent behavior I noticed: just running arecord
will prevent me from changing the frequency, but if I run arecord and stream
video, then it is suddenly OK to change the frequency.
How are you changing frequency? I want to duplicate what you are doing.
v4l2-ctl -f <freq>
I am not seeing the inconsistent behavior. Here are my results.
1. Started acecord and while it is running:
arecord -M -D plughw:2,0 -c2 -f S16_LE -t wav foo.wav
Recording WAVE 'foo.wav' : Signed 16 bit Little Endian, Rate 8000 Hz, Stereo
2. Ran v4l2-ctl -f as follows:
v4l2-ctl -f 700
VIDIOC_G_TUNER: failed: Device or resource busy
VIDIOC_S_FREQUENCY: failed: Device or resource busy
Based on the current implementation, it failed with resource
busy as expected.
3. Started v4l2-ctl as follows:
v4l2-ctl --stream-mmap --stream-count=100 -d /dev/video0
VIDIOC_STREAMON: failed: Device or resource busy
shuah@deneb:/mnt/data/lkml/v4l-utils/utils/v4l2-ctl$ v4l2-ctl -f 700
VIDIOC_G_TUNER: failed: Device or resource busy
VIDIOC_S_FREQUENCY: failed: Device or resource busy
Based on the current implementation, it failed with resource
busy as expected.
4. After stopping arecord:
v4l2-ctl --stream-mmap --stream-count=100 -d /dev/video0
<<<<<<<<<<<<< 11.88 fps
<<<<<<<<<<<<<<< 13.36 fps
<<<<<<<<<<<<<<< 14.00 fps
<<<<<<<<<<<<<<<< 14.35 fps
<<<<<<<<<<<<<<< 14.57 fps
<<<<<<<<<<<<<<<< 14.71 fps
<<<<<<<<<
Worked as expected.
5. After stopping above video streaming:
arecord -M -D plughw:2,0 -c2 -f S16_LE -t wav foo.wav
Recording WAVE 'foo.wav' : Signed 16 bit Little Endian, Rate 8000 Hz, Stereo
Worked as expected.
BTW, I think there was also inconsistent behavior in the order of streaming
audio and video: if I stream video first, then I can stream audio afterwards.
But if I stream audio first, then (if I remember correctly) I can't start
video streaming.
Okay this is what I saw:
While v4l2-ctl --stream-mmap --stream-count=100 -d /dev/video0
I could start arecord -M -D plughw:2,0 -c2 -f S16_LE -t wav foo.wav
I ran strace on v4l2-ctl --stream-mmap --stream-count=100 -d /dev/video0
and I didn't see AUDIO holds. The only think of here is that
v4l2-ctl --stream-mmap --stream-count=100 -d /dev/video0
doesn't open audio device. I didn't see this when tested with other
video apps, (tvtine, xawtv, vlc). When video is streaming, I see
arecord failing with device busy.
As far I can see, exclusion logic is working correctly. s_freq does
fail now based on the current logic.
btw I tested all of this on 5.0-rc4
thanks,
-- Shuah