[Alsa Document]3, platform.txt

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最新推荐文章于 2024-08-24 08:58:32 发布

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本文深入探讨了ASoC Platform Driver的结构和功能，包括音频DMA驱动程序，SoC DAI驱动程序和DSP驱动程序的详细描述。讲解了平台驱动程序如何针对SoCCPU工作，以及它在ALSA操作中的角色。

从[Alsa Document]1, overall.txt的描述中我们了解到Alsa分为三部分，分别是:
<1> codec driver
<2> platform driver
<3> Machine driver

本篇来介绍platform driver
基于4.9.123版本内核 Documentation/sound/alsa/soc/platform.txt

ASoC Platform Driver
====================

An ASoC platform driver class can be divided into audio DMA drivers, SoC DAI
drivers and DSP drivers. The platform drivers only target the SoC CPU and must
have no board specific code.
ASoC platform 驱动程序类可分为音频DMA驱动程序，SoC DAI驱动程序和DSP驱动程序。 
platform 驱动程序仅针对SoC CPU，并且必须没有特定于板的代码。

Audio DMA
=========

The platform DMA driver optionally supports the following ALSA operations:-
platform DMA驱动程序可选择支持以下ALSA操作： - 

/* SoC audio ops */
struct snd_soc_ops {
  int (*startup)(struct snd_pcm_substream *);
  void (*shutdown)(struct snd_pcm_substream *);
  int (*hw_params)(struct snd_pcm_substream *, struct snd_pcm_hw_params *);
  int (*hw_free)(struct snd_pcm_substream *);
  int (*prepare)(struct snd_pcm_substream *);
  int (*trigger)(struct snd_pcm_substream *, int);
};

The platform driver exports its DMA functionality via struct snd_soc_platform_driver:-
平台驱动程序通过struct snd_soc_platform_driver导出其DMA功能： - 

struct snd_soc_platform_driver {
  char *name;

  int (*probe)(struct platform_device *pdev);
  int (*remove)(struct platform_device *pdev);
  int (*suspend)(struct platform_device *pdev, struct snd_soc_cpu_dai *cpu_dai);
  int (*resume)(struct platform_device *pdev, struct snd_soc_cpu_dai *cpu_dai);

  /* pcm creation and destruction */
  int (*pcm_new)(struct snd_card *, struct snd_soc_codec_dai *, struct snd_pcm *);
  void (*pcm_free)(struct snd_pcm *);

  /*
   * For platform caused delay reporting.
   * Optional.
   */
  snd_pcm_sframes_t (*delay)(struct snd_pcm_substream *,
    struct snd_soc_dai *);

  /* platform stream ops */
  struct snd_pcm_ops *pcm_ops;
};

Please refer to the ALSA driver documentation for details of audio DMA.
有关音频DMA的详细信息，请参阅ALSA驱动程序文档。
http://www.alsa-project.org/~iwai/writing-an-alsa-driver/

An example DMA driver is soc/pxa/pxa2xx-pcm.c

SoC DAI Drivers
===============

Each SoC DAI driver must provide the following features:-
每个SoC DAI驱动程序*必须*提供以下功能： - 

 1) Digital audio interface (DAI) description	数字音频接口（DAI）描述
 2) Digital audio interface configuration			数字音频接口（DAI）配置
 3) PCM's description										PCM的描述
 4) SYSCLK configuration								SYSCLK 的描述
 5) Suspend and resume (optional)					可选的暂停和恢复操作

Please see codec.txt for a description of items 1 - 4.
请参考codec.txt中项目1 - 4的描述

SoC DSP Drivers
===============

Each SoC DSP driver usually supplies the following features :-
每个SoC DSP驱动程序通常提供以下功能： - 

 1) DAPM graph		DAPM图形
 2) Mixer controls	调音器控制
 3) DMA IO to/from DSP buffers (if applicable)			DMA IO收发DSP的buffer（如果可用）
 4) Definition of DSP front end (FE) PCM devices.		DSP 前后端的PCM定义

Please see DPCM.txt for a description of item 4.
请参考DPCM.txt中对项目4的描述