linux-kernel - Re: [PATCH v10 0/4] Media Device Allocator API

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Date:   Fri, 25 Jan 2019 17:19:00 -0700
From:   shuah <shuah@...nel.org>
To:     Sakari Ailus <sakari.ailus@....fi>
Cc:     mchehab@...nel.org, perex@...ex.cz, tiwai@...e.com,
        hverkuil@...all.nl, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
        shuah <shuah@...nel.org>
Subject: Re: [PATCH v10 0/4] Media Device Allocator API

Hi Sakari,

On 1/25/19 8:28 AM, Sakari Ailus wrote:
> Hi Shuah,
> 
> On Thu, Jan 24, 2019 at 01:32:37PM -0700, 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.
> 
> Thanks for the update. I have to apologise I haven't ended up reviewing the
> set for some time. After taking a look at the current version, I'm happy to
> see that a number of issues recognised during earlier review rounds have
> been addressed.
> 
> Would you happen to have a media graph (media-ctl --print-dot and media-ctl
> -p) from the device? That'd help understanding the device a bit better for
> those who are not familiar with it.
> 

Please see the attached files for the below. It came in very handy
for testing partial graphs as I did bind and unbind of the drivers
in this mix.

media-ctl --print-dot and
media-ctl --print-topology

thanks,
-- Shuah

View attachment "media_graph_topo" of type "text/plain" (87218 bytes)

Download attachment "media_graph.dot" of type "application/msword-template" (63098 bytes)