389 lines
13 KiB
ReStructuredText
389 lines
13 KiB
ReStructuredText
|
===========
|
||
|
|
Dynamic PCM
|
||
|
|
===========
|
||
|
|
|
||
|
|
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
|
||
|
|
digital audio to I2S DAI0, I2S DAI1 or PDM DAI2. This is useful for on SoC DSP
|
||
|
|
drivers that expose several ALSA PCMs and can route to multiple DAIs.
|
||
|
|
|
||
|
|
The DPCM runtime routing is determined by the ALSA mixer settings in the same
|
||
|
|
way as the analog signal is routed in an ASoC codec driver. DPCM uses a DAPM
|
||
|
|
graph representing the DSP internal audio paths and uses the mixer settings to
|
||
|
|
determine the path used by each ALSA PCM.
|
||
|
|
|
||
|
|
DPCM re-uses all the existing component codec, platform and DAI drivers without
|
||
|
|
any modifications.
|
||
|
|
|
||
|
|
|
||
|
|
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 |
|
||
|
|
|
||
|
|
*************
|
||
|
|
PCM0 <------------> * * <----DAI0-----> Codec Headset
|
||
|
|
* *
|
||
|
|
PCM1 <------------> * * <----DAI1-----> Codec Speakers
|
||
|
|
* DSP *
|
||
|
|
PCM2 <------------> * * <----DAI2-----> MODEM
|
||
|
|
* *
|
||
|
|
PCM3 <------------> * * <----DAI3-----> BT
|
||
|
|
* *
|
||
|
|
* * <----DAI4-----> DMIC
|
||
|
|
* *
|
||
|
|
* * <----DAI5-----> FM
|
||
|
|
*************
|
||
|
|
|
||
|
|
This diagram shows a simple smart phone audio subsystem. It supports Bluetooth,
|
||
|
|
FM digital radio, Speakers, Headset Jack, digital microphones and cellular
|
||
|
|
modem. This sound card exposes 4 DSP front end (FE) ALSA PCM devices and
|
||
|
|
supports 6 back end (BE) DAIs. Each FE PCM can digitally route audio data to any
|
||
|
|
of the BE DAIs. The FE PCM devices can also route audio to more than 1 BE DAI.
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
Example - DPCM Switching playback from DAI0 to DAI1
|
||
|
|
---------------------------------------------------
|
||
|
|
|
||
|
|
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
|
||
|
|
* *
|
||
|
|
PCM1 <------------> * * <----DAI1-----> Codec Speakers
|
||
|
|
* DSP *
|
||
|
|
PCM2 <------------> * * <----DAI2-----> MODEM
|
||
|
|
* *
|
||
|
|
PCM3 <------------> * * <----DAI3-----> BT
|
||
|
|
* *
|
||
|
|
* * <----DAI4-----> DMIC
|
||
|
|
* *
|
||
|
|
* * <----DAI5-----> FM
|
||
|
|
*************
|
||
|
|
|
||
|
|
The headset is removed from the jack by user so the speakers must now be used :-
|
||
|
|
::
|
||
|
|
|
||
|
|
*************
|
||
|
|
PCM0 <============> * * <----DAI0-----> Codec Headset
|
||
|
|
* *
|
||
|
|
PCM1 <------------> * * <====DAI1=====> Codec Speakers
|
||
|
|
* DSP *
|
||
|
|
PCM2 <------------> * * <----DAI2-----> MODEM
|
||
|
|
* *
|
||
|
|
PCM3 <------------> * * <----DAI3-----> BT
|
||
|
|
* *
|
||
|
|
* * <----DAI4-----> DMIC
|
||
|
|
* *
|
||
|
|
* * <----DAI5-----> FM
|
||
|
|
*************
|
||
|
|
|
||
|
|
The audio driver processes this as follows :-
|
||
|
|
|
||
|
|
1. Machine driver receives Jack removal event.
|
||
|
|
|
||
|
|
2. Machine driver OR audio HAL disables the Headset path.
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
5. DPCM runs the PCM ops for startup(), hw_params(), prepare() 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
|
||
|
|
and then DPCM will take care of managing the DAI PCM operations to either bring
|
||
|
|
the link up or down. Audio playback does not stop during this transition.
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
2. Define any FE/BE PCM operations.
|
||
|
|
|
||
|
|
3. Define widget graph connections.
|
||
|
|
|
||
|
|
|
||
|
|
FE and BE DAI links
|
||
|
|
-------------------
|
||
|
|
::
|
||
|
|
|
||
|
|
| Front End PCMs | SoC DSP | Back End DAIs | Audio devices |
|
||
|
|
|
||
|
|
*************
|
||
|
|
PCM0 <------------> * * <----DAI0-----> Codec Headset
|
||
|
|
* *
|
||
|
|
PCM1 <------------> * * <----DAI1-----> Codec Speakers
|
||
|
|
* DSP *
|
||
|
|
PCM2 <------------> * * <----DAI2-----> MODEM
|
||
|
|
* *
|
||
|
|
PCM3 <------------> * * <----DAI3-----> BT
|
||
|
|
* *
|
||
|
|
* * <----DAI4-----> DMIC
|
||
|
|
* *
|
||
|
|
* * <----DAI5-----> FM
|
||
|
|
*************
|
||
|
|
|
||
|
|
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[] = {
|
||
|
|
{
|
||
|
|
.name = "PCM0 System",
|
||
|
|
.stream_name = "System Playback",
|
||
|
|
.cpu_dai_name = "System Pin",
|
||
|
|
.platform_name = "dsp-audio",
|
||
|
|
.codec_name = "snd-soc-dummy",
|
||
|
|
.codec_dai_name = "snd-soc-dummy-dai",
|
||
|
|
.dynamic = 1,
|
||
|
|
.trigger = {SND_SOC_DPCM_TRIGGER_POST, SND_SOC_DPCM_TRIGGER_POST},
|
||
|
|
.dpcm_playback = 1,
|
||
|
|
},
|
||
|
|
.....< other FE and BE DAI links here >
|
||
|
|
};
|
||
|
|
|
||
|
|
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``
|
||
|
|
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
|
||
|
|
start and stop sequences).
|
||
|
|
|
||
|
|
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 >
|
||
|
|
{
|
||
|
|
.name = "Codec Headset",
|
||
|
|
.cpu_dai_name = "ssp-dai.0",
|
||
|
|
.platform_name = "snd-soc-dummy",
|
||
|
|
.no_pcm = 1,
|
||
|
|
.codec_name = "rt5640.0-001c",
|
||
|
|
.codec_dai_name = "rt5640-aif1",
|
||
|
|
.ignore_suspend = 1,
|
||
|
|
.ignore_pmdown_time = 1,
|
||
|
|
.be_hw_params_fixup = hswult_ssp0_fixup,
|
||
|
|
.ops = &haswell_ops,
|
||
|
|
.dpcm_playback = 1,
|
||
|
|
.dpcm_capture = 1,
|
||
|
|
},
|
||
|
|
.....< other BE DAI links here >
|
||
|
|
};
|
||
|
|
|
||
|
|
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 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
|
||
|
|
* *
|
||
|
|
PCM1 <------------> * * <----DAI1-----> Codec Speakers
|
||
|
|
* DSP *
|
||
|
|
PCM2 <------------> * * <====DAI2=====> MODEM
|
||
|
|
* *
|
||
|
|
PCM3 <------------> * * <====DAI3=====> BT
|
||
|
|
* *
|
||
|
|
* * <----DAI4-----> DMIC
|
||
|
|
* *
|
||
|
|
* * <----DAI5-----> FM
|
||
|
|
*************
|
||
|
|
|
||
|
|
This allows the host CPU to sleep while the DSP, MODEM DAI and the BT DAI are
|
||
|
|
still in operation.
|
||
|
|
|
||
|
|
A BE DAI link can also set the codec to a dummy device if the codec is a device
|
||
|
|
that is managed externally.
|
||
|
|
|
||
|
|
Likewise a BE DAI can also set a dummy cpu DAI if the CPU DAI is managed by the
|
||
|
|
DSP firmware.
|
||
|
|
|
||
|
|
|
||
|
|
FE/BE PCM operations
|
||
|
|
--------------------
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
e.g. DSP converts all FE hw params to run at fixed rate of 48k, 16bit, stereo for
|
||
|
|
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)
|
||
|
|
{
|
||
|
|
struct snd_interval *rate = hw_param_interval(params,
|
||
|
|
SNDRV_PCM_HW_PARAM_RATE);
|
||
|
|
struct snd_interval *channels = hw_param_interval(params,
|
||
|
|
SNDRV_PCM_HW_PARAM_CHANNELS);
|
||
|
|
|
||
|
|
/* The DSP will convert the FE rate to 48k, stereo */
|
||
|
|
rate->min = rate->max = 48000;
|
||
|
|
channels->min = channels->max = 2;
|
||
|
|
|
||
|
|
/* set DAI0 to 16 bit */
|
||
|
|
params_set_format(params, SNDRV_PCM_FORMAT_S16_LE);
|
||
|
|
return 0;
|
||
|
|
}
|
||
|
|
|
||
|
|
The other PCM operation are the same as for regular DAI links. Use as necessary.
|
||
|
|
|
||
|
|
|
||
|
|
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"},
|
||
|
|
{"AIF1 Playback", NULL, "DAI0 CODEC OUT"},
|
||
|
|
|
||
|
|
|
||
|
|
Writing a DPCM DSP driver
|
||
|
|
=========================
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
2. DAPM graph showing DSP audio routing from FE DAIs to BEs.
|
||
|
|
|
||
|
|
3. DAPM widgets from DSP graph.
|
||
|
|
|
||
|
|
4. Mixers for gains, routing, etc.
|
||
|
|
|
||
|
|
5. DMA configuration.
|
||
|
|
|
||
|
|
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),
|
||
|
|
|
||
|
|
The BE AIF are used to connect the DSP graph to the graphs for the other
|
||
|
|
component drivers (e.g. codec graph).
|
||
|
|
|
||
|
|
|
||
|
|
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
|
||
|
|
* *
|
||
|
|
PCM1 <------------> * * <====DAI1=====> Codec Speakers/Mic
|
||
|
|
* DSP *
|
||
|
|
PCM2 <------------> * * <====DAI2=====> MODEM
|
||
|
|
* *
|
||
|
|
PCM3 <------------> * * <----DAI3-----> BT
|
||
|
|
* *
|
||
|
|
* * <----DAI4-----> DMIC
|
||
|
|
* *
|
||
|
|
* * <----DAI5-----> FM
|
||
|
|
*************
|
||
|
|
|
||
|
|
In this case the PCM data is routed via the DSP. The host CPU in this use case
|
||
|
|
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
|
||
|
|
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
|
||
|
|
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
|
||
|
|
unless your HW needs more fine grained sequencing of the PCM ops.
|
||
|
|
|
||
|
|
|
||
|
|
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,
|
||
|
|
.rate_min = 8000,
|
||
|
|
.rate_max = 8000,
|
||
|
|
.channels_min = 2,
|
||
|
|
.channels_max = 2,
|
||
|
|
};
|
||
|
|
|
||
|
|
static struct snd_soc_dai_link dais[] = {
|
||
|
|
< ... more DAI links above ... >
|
||
|
|
{
|
||
|
|
.name = "MODEM",
|
||
|
|
.stream_name = "MODEM",
|
||
|
|
.cpu_dai_name = "dai2",
|
||
|
|
.codec_dai_name = "modem-aif1",
|
||
|
|
.codec_name = "modem",
|
||
|
|
.dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF
|
||
|
|
| SND_SOC_DAIFMT_CBM_CFM,
|
||
|
|
.params = &dai_params,
|
||
|
|
}
|
||
|
|
< ... more DAI links here ... >
|
||
|
|
|
||
|
|
These parameters are used to configure the DAI hw_params() when DAPM detects a
|
||
|
|
valid path and then calls the PCM operations to start the link. DAPM will also
|
||
|
|
call the appropriate PCM operations to disable the DAI when the path is no
|
||
|
|
longer valid.
|
||
|
|
|
||
|
|
|
||
|
|
Hostless FE
|
||
|
|
-----------
|
||
|
|
|
||
|
|
The DAI link(s) are enabled by a FE that does not read or write any PCM data.
|
||
|
|
This means creating a new FE that is connected with a virtual path to both
|
||
|
|
DAI links. The DAI links will be started when the FE PCM is started and stopped
|
||
|
|
when the FE PCM is stopped. Note that the FE PCM cannot read or write data in
|
||
|
|
this configuration.
|