Messages in this thread | | | Subject | Re: [PATCH v10 0/4] Media Device Allocator API | From | shuah <> | Date | Mon, 28 Jan 2019 16:48:49 -0700 |
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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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