On 1/19/19 3:30 AM, Hans Verkuil wrote:
On 01/19/2019 02:03 AM, shuah wrote:
On 1/18/19 2:54 PM, shuah wrote:
On 1/18/19 1:36 AM, Hans Verkuil wrote:
On 12/18/18 6:59 PM, shuah@xxxxxxxxxx wrote:
From: Shuah Khan <shuah@xxxxxxxxxx>
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.
Change the ALSA driver to use the Media Controller API to share media
resources with DVB, and V4L2 drivers on a AU0828 media device.
The Media Controller specific initialization is done after sound card is
registered. ALSA creates Media interface and entity function graph nodes
for Control, Mixer, PCM Playback, and PCM Capture devices.
snd_usb_hw_params() will call Media Controller enable source handler
interface to request the media resource. If resource request is granted,
it will release it from snd_usb_hw_free(). If resource is busy,
-EBUSY is
returned.
Media specific cleanup is done in usb_audio_disconnect().
Signed-off-by: Shuah Khan <shuah@xxxxxxxxxx>
---
sound/usb/Kconfig | 4 +
sound/usb/Makefile | 2 +
sound/usb/card.c | 14 ++
sound/usb/card.h | 3 +
sound/usb/media.c | 321 +++++++++++++++++++++++++++++++++++++++
sound/usb/media.h | 74 +++++++++
sound/usb/mixer.h | 3 +
sound/usb/pcm.c | 29 +++-
sound/usb/quirks-table.h | 1 +
sound/usb/stream.c | 2 +
sound/usb/usbaudio.h | 6 +
11 files changed, 455 insertions(+), 4 deletions(-)
create mode 100644 sound/usb/media.c
create mode 100644 sound/usb/media.h
<snip>
+int snd_media_device_create(struct snd_usb_audio *chip,
+ struct usb_interface *iface)
+{
+ struct media_device *mdev;
+ struct usb_device *usbdev = interface_to_usbdev(iface);
+ int ret;
+
+ /* usb-audio driver is probed for each usb interface, and
+ * there are multiple interfaces per device. Avoid calling
+ * media_device_usb_allocate() each time usb_audio_probe()
+ * is called. Do it only once.
+ */
+ if (chip->media_dev)
+ goto snd_mixer_init;
+
+ mdev = media_device_usb_allocate(usbdev, KBUILD_MODNAME);
+ if (!mdev)
+ return -ENOMEM;
+
+ if (!media_devnode_is_registered(mdev->devnode)) {
It looks like you missed my comment for v8:
"You should first configure the media device before registering it."
In other words, first create the media entities, and only then do you
register the media device. Otherwise it will come up without any alsa
entities, which are then added. So an application that immediately
opens the media device upon creation will see a topology that is still
in flux.
Yes. You are right. I saw your comment and thought I got it addressed.
I will fix it. I have the logic correct in au0828, but not here.
One thing to mention here is some ALSA entities get created dynamically
during PCM open when stream is initialized. This happens after media
device is registered. These get deleted when pcm close happens. There is
no way to avoid creating entities after media device register.
That's OK. We're missing some infrastructure (media events) to inform the
application about topology changes.
But when registering the media device for the first time it is good practice
to do that after creating all the entities that you can.
Great. We have the same understanding. I think at least one mixer
controller entries can be created prior to registering the media
device. I am working on v10 to do that. Sorry I misread init sequence
in this patch the flow the first time around for v9.
thanks,
-- Shuah
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