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diff --git a/Documentation/sound/alsa/soc/platform.txt b/Documentation/sound/alsa/soc/platform.txt
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+ASoC Platform Driver
+====================
+
+An ASoC platform driver can be divided into audio DMA and SoC DAI configuration
+and control. The platform drivers only target the SoC CPU and must have no board
+specific code.
+
+Audio DMA
+=========
+
+The platform DMA driver optionally supports the following alsa operations:-
+
+/* 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 it's DMA functionailty via struct snd_soc_platform:-
+
+struct snd_soc_platform {
+        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 *);
+
+        /* platform stream ops */
+        struct snd_pcm_ops *pcm_ops;
+};
+
+Please refer to the alsa driver documentation for details of audio DMA.
+http://www.alsa-project.org/~iwai/writing-an-alsa-driver/c436.htm
+
+An example DMA driver is soc/pxa/pxa2xx-pcm.c
+
+
+SoC DAI Drivers
+===============
+
+Each SoC DAI driver must provide the following features:-
+
+ 1) Digital audio interface (DAI) description
+ 2) Digital audio interface configuration
+ 3) PCM's description
+ 4) Sysclk configuration
+ 5) Suspend and resume (optional)
+
+Please see codec.txt for a description of items 1 - 4.