linux-kernel - Re: [alsa-devel] [PATCH 2/5 v4] drm/i2c/adv7511: Add audio support

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Date:	Mon, 11 Apr 2016 15:08:39 +0100
From:	Jose Abreu <Jose.Abreu@...opsys.com>
To:	Lars-Peter Clausen <lars@...afoo.de>,
	Jose Abreu <Jose.Abreu@...opsys.com>,
	<linux-snps-arc@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
	<alsa-devel@...a-project.org>
CC:	<architt@...eaurora.org>, <airlied@...ux.ie>,
	<Vineet.Gupta1@...opsys.com>, <Alexey.Brodkin@...opsys.com>,
	<lgirdwood@...il.com>, <CARLOS.PALMINHA@...opsys.com>,
	<broonie@...nel.org>, <tiwai@...e.com>
Subject: Re: [alsa-devel] [PATCH 2/5 v4] drm/i2c/adv7511: Add audio support

Hi Lars,


On 11-04-2016 13:23, Lars-Peter Clausen wrote:
> On 04/11/2016 01:32 PM, Jose Abreu wrote:
>> Hi Lars,
>>
>>
>> On 11-04-2016 10:33, Lars-Peter Clausen wrote:
>>> On 04/11/2016 11:27 AM, Jose Abreu wrote:
>>>> Hi Lars,
>>>>
>>>>
>>>> On 09-04-2016 16:02, Lars-Peter Clausen wrote:
>>>>> On 04/08/2016 06:12 PM, Jose Abreu wrote:
>>>>> [...]
>>>>>>> [...]
>>>>>>>> +- adi,enable-audio: If set the ADV7511 driver will register a codec interface
>>>>>>>> +  into ALSA SoC.
>>>>>>> This is not a description of the hardware.
>>>>>> Is this okay: "adi,enable-audio: Set this boolean parameter if ADV7511
>>>>>> transmitter routes audio signals" ?
>>>>> I don't think we need this property. There is no problem with registering
>>>>> the audio part unconditionally. As long as there is no connection we wont
>>>>> create a sound card that is exposed to userspace.
>>>>>
>>>> This change was suggested by Laurent Pinchart and was introduced in v3. Quoting
>>>> Laurent:
>>>> "The idea is that enabling support for ADV7511 audio in the kernel isn't coupled
>>>> with whether the system includes audio support. It would be confusing, and would
>>>> also waste resources, to create a Linux sound device when no sound channel is
>>>> routed on the board."
>>> I wouldn't care too much about this at this point, the extra amount of
>>> resources required for registering the CODEC (but not the sound card) is
>>> just a few bytes (sizeof(struct snd_soc_codec)).
>>>
>>> Nevertheless what we should do is describe the hardware and from this
>>> information infer whether there is a audio connection or not and if there is
>>> none we might skip registering the CODEC. In my opinion this hardware
>>> description should be modeled using of-graph, having a connection between
>>> the SoC side and the adv7511 SPDIF or I2S port.
>>>
>> You mean something like this:
>>
>> sound_playback: sound_playback {
>>     compatible = "simple-audio-card";
>>     [...]
>>     simple-audio-card,format = "i2s";
>>     [...]
>> }
>>
>> adv7511@xx {
>>     compatible = "adi,adv7511";
>>     [...]
>>
>>     ports {
>>         [...]
>>         /* Audio Output */
>>         port@x {
>>             reg = <x>;
>>             endpoint {
>>                 remote-endpoint = <&sound_playback>;
>>             }
>>         }
>>     }
>> }
> Yes, something like that. Not exactly like that, but similar. One of the
> core concepts of of-graph is that there is always a description of the
> connection from both sides, this way each side can independently figure out
> where it is connected.
>
> Currently there is also zero support of of-graph in ASoC, so a bit of work
> is required to get this integrated properly.
>

I also believe this would be the better option but in the meantime can't I
integrate the audio like it is being done in the dw-hdmi driver[1]? In this
driver the audio is registered as a sound card and is conditionally built using
Kconfig, just like I was doing in the previous versions. I know you said the
HDMI audio is still an open issue but it seems that for this case it was accepted.

[1] http://lxr.free-electrons.com/source/drivers/gpu/drm/bridge/dw-hdmi-ahb-audio.c

Best regards,
Jose Miguel Abreu