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Commit 40433cd3 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ASoC: doc: ReSTize DPCM.txt 



A simple conversion from a plain text file.
The file name was renamed to lower letters to align with others.

Acked-by: default avatarMark Brown <broonie@kernel.org>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 8155258a

Documentation/sound/alsa/soc/DPCM.txt→Documentation/sound/soc/dpcm.rst

+146 −134
Original line number Diff line number Diff line 
===========

Dynamic PCM

===========



1. Description

==============

Description

===========



Dynamic PCM allows an ALSA PCM device to digitally route its PCM audio to

various digital endpoints during the PCM stream runtime. e.g. PCM0 can route
@@ -23,6 +24,7 @@ Phone Audio System with SoC based DSP 


Consider the following phone audio subsystem. This will be used in this

document for all examples :-

::



  | Front End PCMs    |  SoC DSP  | Back End DAIs | Audio devices |
@@ -55,6 +57,7 @@ Audio is being played to the Headset. After a while the user removes the headset 
and audio continues playing on the speakers.



Playback on PCM0 to Headset would look like :-

::



                      *************

  PCM0 <============> *           * <====DAI0=====> Codec Headset
@@ -71,6 +74,7 @@ PCM3 <------------> * * <----DAI3-----> BT 
                      *************



The headset is removed from the jack by user so the speakers must now be used :-

::



                      *************

  PCM0 <============> *           * <----DAI0-----> Codec Headset
@@ -88,16 +92,16 @@ PCM3 <------------> * * <----DAI3-----> BT 


The audio driver processes this as follows :-



 1) Machine driver receives Jack removal event.

1. Machine driver receives Jack removal event.



 2) Machine driver OR audio HAL disables the Headset path.

2. Machine driver OR audio HAL disables the Headset path.



 3) DPCM runs the PCM trigger(stop), hw_free(), shutdown() operations on DAI0

3. DPCM runs the PCM trigger(stop), hw_free(), shutdown() operations on DAI0

   for headset since the path is now disabled.



 4) Machine driver or audio HAL enables the speaker path.

4. Machine driver or audio HAL enables the speaker path.



 5) DPCM runs the PCM ops for startup(), hw_params(), prepapre() and

5. DPCM runs the PCM ops for startup(), hw_params(), prepapre() and

   trigger(start) for DAI1 Speakers since the path is enabled.



In this example, the machine driver or userspace audio HAL can alter the routing
@@ -112,15 +116,16 @@ DPCM machine driver 
The DPCM enabled ASoC machine driver is similar to normal machine drivers

except that we also have to :-



 1) Define the FE and BE DAI links.

1. Define the FE and BE DAI links.



 2) Define any FE/BE PCM operations.

2. Define any FE/BE PCM operations.



 3) Define widget graph connections.

3. Define widget graph connections.





1 FE and BE DAI links

---------------------

FE and BE DAI links

-------------------

::



  | Front End PCMs    |  SoC DSP  | Back End DAIs | Audio devices |
@@ -140,6 +145,7 @@ PCM3 <------------> * * <----DAI3-----> BT 


For the example above we have to define 4 FE DAI links and 6 BE DAI links. The

FE DAI links are defined as follows :-

::



  static struct snd_soc_dai_link machine_dais[] = {

	{
@@ -157,8 +163,8 @@ static struct snd_soc_dai_link machine_dais[] = { 
  };



This FE DAI link is pretty similar to a regular DAI link except that we also

set the DAI link to a DPCM FE with the "dynamic = 1". The supported FE stream

directions should also be set with the "dpcm_playback" and "dpcm_capture"

set the DAI link to a DPCM FE with the ``dynamic = 1``. The supported FE stream

directions should also be set with the ``dpcm_playback`` and ``dpcm_capture``

flags. There is also an option to specify the ordering of the trigger call for

each FE. This allows the ASoC core to trigger the DSP before or after the other

components (as some DSPs have strong requirements for the ordering DAI/DSP
@@ -168,6 +174,7 @@ The FE DAI above sets the codec and code DAIs to dummy devices since the BE is 
dynamic and will change depending on runtime config.



The BE DAIs are configured as follows :-

::



  static struct snd_soc_dai_link machine_dais[] = {

	.....< FE DAI links here >
@@ -189,12 +196,13 @@ static struct snd_soc_dai_link machine_dais[] = { 
  };



This BE DAI link connects DAI0 to the codec (in this case RT5460 AIF1). It sets

the "no_pcm" flag to mark it has a BE and sets flags for supported stream

directions using "dpcm_playback" and "dpcm_capture" above.

the ``no_pcm`` flag to mark it has a BE and sets flags for supported stream

directions using ``dpcm_playback`` and ``dpcm_capture`` above.



The BE has also flags set for ignoring suspend and PM down time. This allows

the BE to work in a hostless mode where the host CPU is not transferring data

like a BT phone call :-

::



                      *************

  PCM0 <------------> *           * <----DAI0-----> Codec Headset
@@ -220,10 +228,10 @@ Likewise a BE DAI can also set a dummy cpu DAI if the CPU DAI is managed by the 
DSP firmware.





2 FE/BE PCM operations

----------------------

FE/BE PCM operations

--------------------



The BE above also exports some PCM operations and a "fixup" callback. The fixup

The BE above also exports some PCM operations and a ``fixup`` callback. The fixup

callback is used by the machine driver to (re)configure the DAI based upon the

FE hw params. i.e. the DSP may perform SRC or ASRC from the FE to BE.
@@ -231,6 +239,7 @@ e.g. DSP converts all FE hw params to run at fixed rate of 48k, 16bit, stereo fo 
DAI0. This means all FE hw_params have to be fixed in the machine driver for

DAI0 so that the DAI is running at desired configuration regardless of the FE

configuration.

::



  static int dai0_fixup(struct snd_soc_pcm_runtime *rtd,

			struct snd_pcm_hw_params *params)
@@ -254,12 +263,13 @@ static int dai0_fixup(struct snd_soc_pcm_runtime *rtd, 
The other PCM operation are the same as for regular DAI links. Use as necessary.





3 Widget graph connections

--------------------------

Widget graph connections

------------------------



The BE DAI links will normally be connected to the graph at initialisation time

by the ASoC DAPM core. However, if the BE codec or BE DAI is a dummy then this

has to be set explicitly in the driver :-

::



  /* BE for codec Headset -  DAI0 is dummy and managed by DSP FW */

  {"DAI0 CODEC IN", NULL, "AIF1 Capture"},
@@ -273,21 +283,22 @@ The DPCM DSP driver looks much like a standard platform class ASoC driver 
combined with elements from a codec class driver. A DSP platform driver must

implement :-



 1) Front End PCM DAIs - i.e. struct snd_soc_dai_driver.

1. Front End PCM DAIs - i.e. struct snd_soc_dai_driver.



 2) DAPM graph showing DSP audio routing from FE DAIs to BEs.

2. DAPM graph showing DSP audio routing from FE DAIs to BEs.



 3) DAPM widgets from DSP graph.

3. DAPM widgets from DSP graph.



 4) Mixers for gains, routing, etc.

4. Mixers for gains, routing, etc.



 5) DMA configuration.

5. DMA configuration.



 6) BE AIF widgets.

6. BE AIF widgets.



Items 6 is important for routing the audio outside of the DSP. AIF need to be

defined for each BE and each stream direction. e.g for BE DAI0 above we would

have :-

::



  SND_SOC_DAPM_AIF_IN("DAI0 RX", NULL, 0, SND_SOC_NOPM, 0, 0),

  SND_SOC_DAPM_AIF_OUT("DAI0 TX", NULL, 0, SND_SOC_NOPM, 0, 0),
@@ -301,7 +312,7 @@ Hostless PCM streams 


A hostless PCM stream is a stream that is not routed through the host CPU. An

example of this would be a phone call from handset to modem.



::



                      *************

  PCM0 <------------> *           * <----DAI0-----> Codec Headset
@@ -322,12 +333,12 @@ is only used for control and can sleep during the runtime of the stream. 


The host can control the hostless link either by :-



 1) Configuring the link as a CODEC <-> CODEC style link. In this case the link

 1. Configuring the link as a CODEC <-> CODEC style link. In this case the link

    is enabled or disabled by the state of the DAPM graph. This usually means

    there is a mixer control that can be used to connect or disconnect the path

    between both DAIs.



 2) Hostless FE. This FE has a virtual connection to the BE DAI links on the DAPM

 2. Hostless FE. This FE has a virtual connection to the BE DAI links on the DAPM

    graph. Control is then carried out by the FE as regular PCM operations.

    This method gives more control over the DAI links, but requires much more

    userspace code to control the link. Its recommended to use CODEC<->CODEC
@@ -339,6 +350,7 @@ CODEC <-> CODEC link 


This DAI link is enabled when DAPM detects a valid path within the DAPM graph.

The machine driver sets some additional parameters to the DAI link i.e.

::



  static const struct snd_soc_pcm_stream dai_params = {

	.formats = SNDRV_PCM_FMTBIT_S32_LE,

Documentation/sound/soc/index.rst

+1 −0
Original line number Diff line number Diff line
@@ -16,3 +16,4 @@ The documentation is spilt into the following sections:- 
   pops-clicks

   clocking

   jack

   dpcm