linux-kernel - Re: [RFC PATCH v8 1/4] media: Media Device Allocator API

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Date:   Sun, 9 Dec 2018 12:37:14 +0100
From:   Pavel Machek <pavel@....cz>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     shuah <shuah@...nel.org>, perex@...ex.cz, tiwai@...e.com,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        alsa-devel@...a-project.org
Subject: Re: [RFC PATCH v8 1/4] media: Media Device Allocator API

Hi!

> > On Thu 2018-12-06 08:33:14, shuah wrote:
> > > On 11/19/18 1:59 AM, Pavel Machek wrote:  
> > > >On Thu 2018-11-01 18:31:30, shuah@...nel.org wrote:  
> > > >>From: Shuah Khan <shuah@...nel.org>
> > > >>
> > > >>Media Device Allocator API to allows multiple drivers share a media device.
> > > >>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.  
> > > >
> > > >Sounds like a ... bad idea?
> > > >
> > > >That's what new "media control" framework is for, no?
> > > >
> > > >Why do you need this?  
> > > 
> > > Media control framework doesn't address this problem of ownership of the
> > > media device when non-media drivers have to own the pipeline. In this case,
> > > snd-usb owns the audio pipeline when an audio application is using the
> > > device. Without this work, media drivers won't be able to tell if snd-usb is
> > > using the tuner and owns the media pipeline.
> > > 
> > > I am going to clarify this in the commit log.  
> > 
> > I guess I'll need the explanation, yes.
> > 
> > How can usb soundcard use the tuner? I thought we'd always have
> > userspace component active and moving data between tuner and usb sound
> > card?
> 
> It sounds that the description of the patch is not 100%, as it seems
> that you're not seeing the hole picture.
> 
> This is designed to solve a very common usecase for media devices
> where one physical device (an USB stick) provides both audio
> and video.

Aha, ok, it makes sense now. Thanks!
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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