Date:	Thu, 16 Oct 2014 16:02:49 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Shuah Khan <shuahkh@....samsung.com>
Cc:	m.chehab@...sung.com, akpm@...ux-foundation.org,
	gregkh@...uxfoundation.org, crope@....fi, olebowle@....com,
	dheitmueller@...nellabs.com, hverkuil@...all.nl,
	ramakrmu@...co.com, sakari.ailus@...ux.intel.com,
	laurent.pinchart@...asonboard.com, perex@...ex.cz,
	prabhakar.csengg@...il.com, tim.gardner@...onical.com,
	linux@...elenboom.it, linux-media@...r.kernel.org,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/6] media token resource framework

At Wed, 15 Oct 2014 14:21:34 -0600,
Shuah Khan wrote:
> 
> On 10/15/2014 10:48 AM, Takashi Iwai wrote:
> > At Tue, 14 Oct 2014 08:58:36 -0600,
> > Shuah Khan wrote:
> >>
> >> Add media token device resource framework to allow sharing
> >> resources such as tuner, dma, audio etc. across media drivers
> >> and non-media sound drivers that control media hardware. The
> >> Media token resource is created at the main struct device that
> >> is common to all drivers that claim various pieces of the main
> >> media device, which allows them to find the resource using the
> >> main struct device. As an example, digital, analog, and
> >> snd-usb-audio drivers can use the media token resource API
> >> using the main struct device for the interface the media device
> >> is attached to.
> >>
> >> This patch series consists of media token resource framework
> >> and changes to use it in dvb-core, v4l2-core, au0828 driver,
> >> and snd-usb-audio driver.
> >>
> >> With these changes dvb and v4l2 can share the tuner without
> >> disrupting each other. Used tvtime, xawtv, kaffeine, and vlc,
> >> vlc audio capture option, arecord/aplay during development to
> >> identify v4l2 vb2 and vb1 ioctls and file operations that
> >> disrupt the digital stream and would require changes to check
> >> tuner ownership prior to changing the tuner configuration.
> >> vb2 changes are made in the v4l2-core and vb1 changes are made
> >> in the au0828 driver to encourage porting drivers to vb2 to
> >> advantage of the new media token resource framework with changes
> >> in the core.
> >>
> >> In this patch v2 series, fixed problems identified in the
> >> patch v1 series. Important ones are changing snd-usb-audio
> >> to use media tokens, holding tuner lock in VIDIOC_ENUMINPUT,
> >> and VIDIOC_QUERYSTD.
> > 
> > Just took a quick glance over the patches, and my first concern is why
> > this has to be lib/*.  This means it's always built-in as long as this
> > config is enabled (and will be so on distro kernel) even if it's not
> > used at all.
> > 
> 
> Right this module gets built when CONFIG_MEDIA_SUPPORT is enabled
> and stubs are in place when it is not enabled. The intent is for
> this feature to be enabled by default when media support is enabled.
> When a driver doesn't create the resource, it will simply not find it
> and for drivers like snd-usb-audio that aren't tried to media support,
> the stubs are in place and feature is essentially disabled.
> 
> I picked lib so this module can be included in non-media drivers
> e.g: snd-usb-audio.
> 
> Does this help explain the design? I didn't want to introduce a new
> config for this feature. If lib isn't right place, could you recommend
> another one that makes this modules available to non-media drivers?
> moving isn't a problem.

We can create a small module depending on CONFIG_MEDIA.  But it'll be
rather a question of the size.  If it's reasonably small and generic
enough, it's worth to put into lib/*, I think.


Takashi
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