[PATCH] ASoC: atmel: atmel-classd: Re-add dai_link->platform to fix card init

[Andrei.Simion at microchip.com]

Hi Kuninori,

On 05.06.2024 02:36, Kuninori Morimoto wrote:
> Hi Andrei
> 
>> The removed dai_link->platform component cause a fail which
>> is exposed at runtime. (ex: when a sound tool is used)
>> This patch re-adds the dai_link->platform component to have
>> a full card registered.
> 
> Thank you for the patch, and sorry to bother you by my patch.
> 
> Acked-by: Kuninori Morimoto <kuninori.morimoto.gx at renesas.com>
> 
> 
> I would like to ask for reference. What is this "sound tool" ?
> (Is it on userland side ? or Kernel side ?)

It is on userland side like : arecord, aplay - command-line sound recorder and player for ALSA soundcard driver or speaker-test - command-line speaker test tone generator for ALSA

> And do you know what it will do to dai_link->platform ?
>

A platform driver is critical for interfacing between userland audio applications and the physical audio hardware. Proper implementation ensures successful audio playback and recording.

On the basic level of how it works when a userland application plays audio:
1. The ALSA subsystem processes the audio stream and sends it to the appropriate driver through the ASoC layer.
2. The dai_link->platform component is responsible for managing the data transfer, using DMA, to the codec (Class D amplifier).
3. The codec driver then converts the digital audio data into a PWM signal or other suitable digital representation that directly drives the loudspeaker.

> Thank you for your help !!
> Best regards
> ---
> Kuninori Morimoto


Best regards,
Andrei Simion