linux-kernel - Re: [PATCH v6 3/3] sound/usb: Use Media Controller API to share media resources

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Date:   Tue, 06 Dec 2016 15:17:23 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Shuah Khan <shuahkh@....samsung.com>
Cc:     mchehab@...nel.org, tiwai@...e.com, perex@...ex.cz,
        hans.verkuil@...co.com, javier@....samsung.com,
        chehabrafael@...il.com, g.liakhovetski@....de, ONeukum@...e.com,
        k@...w.org, daniel@...que.org, mahasler@...il.com,
        clemens@...isch.de, geliangtang@....com, vdronov@...hat.com,
        sakari.ailus@....fi, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, alsa-devel@...a-project.org
Subject: Re: [PATCH v6 3/3] sound/usb: Use Media Controller API to share media resources

Hi Shuah,

On Monday 05 Dec 2016 17:38:23 Shuah Khan wrote:
> On 12/05/2016 04:21 PM, Laurent Pinchart wrote:
> > On Monday 05 Dec 2016 15:44:30 Shuah Khan wrote:
> >> On 11/30/2016 03:01 PM, Shuah Khan wrote:
> >>> Change ALSA driver to use Media Controller API to share media resources
> >>> with DVB, and V4L2 drivers on a AU0828 media device.
> >>> 
> >>> 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 <shuahkh@....samsung.com>
> >> 
> >> Hi Takashi,
> >> 
> >> If you are good with this patch, could you please Ack it, so Mauro
> >> can pull it into media tree with the other two patches in this series,
> >> when he is ready to do so.
> > 
> > I *really* want to address the concerns raised by Sakari before pulling
> > more code that makes fixing the race conditions more difficult. Please,
> > let's all work on fixing the core code to build a stable base on which we
> > can build additional features. V4L2 and MC need teamwork, it's time to
> > give the subsystem the love it deserves.
> 
> Hi Laurent,
> 
> The issue Sakari brought up is specific to using devm for video_device in
> omap3 and vsp1. I tried reproducing the problem on two different drivers
> and couldn't on Linux 4.9-rc7.
> 
> After sharing that with Sakari, I suggested to Sakari to pull up his patch
> that removes the devm usage and see if he still needs all the patches in his
> patch series. He didn't back to me on that. I also requested him to rebase
> on top of media dev allocator because the allocator routines he has don't
> address the shared media device need.
> 
> He also didn't respond to my response regarding the reasons for choosing
> graph_mutex to protect enable_source and disable_source handlers.
> 
> So I am not sure how to move forward at the moment without a concrete plan
> for Sakari's RFC series. Sakari's patch series is still RFC and doesn't
> address shared media_device and requires all drivers to change.

Today is a public holiday in Finland, I don't expect Sakari to be available. 
Let's check this with him tomorrow.

-- 
Regards,

Laurent Pinchart