Documentation/driver-api/soundwire/summary.rst - linux - Git at Google

 ===========================
 SoundWire Subsystem Summary
 ===========================

 SoundWire is a new interface ratified in 2015 by the MIPI Alliance.
 SoundWire is used for transporting data typically related to audio
 functions. SoundWire interface is optimized to integrate audio devices in
 mobile or mobile inspired systems.

 SoundWire is a 2-pin multi-drop interface with data and clock line. It
 facilitates development of low cost, efficient, high performance systems.
 Broad level key features of SoundWire interface include:

  (1) Transporting all of payload data channels, control information, and setup
      commands over a single two-pin interface.

  (2) Lower clock frequency, and hence lower power consumption, by use of DDR
      (Dual Data Rate) data transmission.

  (3) Clock scaling and optional multiple data lanes to give wide flexibility
      in data rate to match system requirements.

  (4) Device status monitoring, including interrupt-style alerts to the Master.

 The SoundWire protocol supports up to eleven Slave interfaces. All the
 interfaces share the common Bus containing data and clock line. Each of the
 Slaves can support up to 14 Data Ports. 13 Data Ports are dedicated to audio
 transport. Data Port0 is dedicated to transport of Bulk control information,
 each of the audio Data Ports (1..14) can support up to 8 Channels in
 transmit or receiving mode (typically fixed direction but configurable
 direction is enabled by the specification).  Bandwidth restrictions to
 ~19.2..24.576Mbits/s don't however allow for 11*13*8 channels to be
 transmitted simultaneously.

 Below figure shows an example of connectivity between a SoundWire Master and
 two Slave devices. ::

         +---------------+                                       +---------------+
         |               |                       Clock Signal    |               |
         |    Master     |-------+-------------------------------|    Slave      |
         |   Interface   |       |               Data Signal     |  Interface 1  |
         |               |-------|-------+-----------------------|               |
         +---------------+       |       |                       +---------------+
                                 |       |
                                 |       |
                                 |       |
                              +--+-------+--+
                              |             |
                              |   Slave     |
                              | Interface 2 |
                              |             |
                              +-------------+


 Terminology
 ===========

 The MIPI SoundWire specification uses the term 'device' to refer to a Master
 or Slave interface, which of course can be confusing. In this summary and
 code we use the term interface only to refer to the hardware. We follow the
 Linux device model by mapping each Slave interface connected on the bus as a
 device managed by a specific driver. The Linux SoundWire subsystem provides
 a framework to implement a SoundWire Slave driver with an API allowing
 3rd-party vendors to enable implementation-defined functionality while
 common setup/configuration tasks are handled by the bus.

 Bus:
 Implements SoundWire Linux Bus which handles the SoundWire protocol.
 Programs all the MIPI-defined Slave registers. Represents a SoundWire
 Master. Multiple instances of Bus may be present in a system.

 Slave:
 Registers as SoundWire Slave device (Linux Device). Multiple Slave devices
 can register to a Bus instance.

 Slave driver:
 Driver controlling the Slave device. MIPI-specified registers are controlled
 directly by the Bus (and transmitted through the Master driver/interface).
 Any implementation-defined Slave register is controlled by Slave driver. In
 practice, it is expected that the Slave driver relies on regmap and does not
 request direct register access.

 Programming interfaces (SoundWire Master interface Driver)
 ==========================================================

 SoundWire Bus supports programming interfaces for the SoundWire Master
 implementation and SoundWire Slave devices. All the code uses the "sdw"
 prefix commonly used by SoC designers and 3rd party vendors.

 Each of the SoundWire Master interfaces needs to be registered to the Bus.
 Bus implements API to read standard Master MIPI properties and also provides
 callback in Master ops for Master driver to implement its own functions that
 provides capabilities information. DT support is not implemented at this
 time but should be trivial to add since capabilities are enabled with the
 ``device_property_`` API.

 The Master interface along with the Master interface capabilities are
 registered based on board file, DT or ACPI.

 Following is the Bus API to register the SoundWire Bus:

 .. code-block:: c

 	int sdw_bus_master_add(struct sdw_bus *bus,
 				struct device *parent,
 				struct fwnode_handle)
 	{
 		sdw_master_device_add(bus, parent, fwnode);

 		mutex_init(&bus->lock);
 		INIT_LIST_HEAD(&bus->slaves);

 		/* Check ACPI for Slave devices */
 		sdw_acpi_find_slaves(bus);

 		/* Check DT for Slave devices */
 		sdw_of_find_slaves(bus);

 		return 0;
 	}

 This will initialize sdw_bus object for Master device. "sdw_master_ops" and
 "sdw_master_port_ops" callback functions are provided to the Bus.

 "sdw_master_ops" is used by Bus to control the Bus in the hardware specific
 way. It includes Bus control functions such as sending the SoundWire
 read/write messages on Bus, setting up clock frequency & Stream
 Synchronization Point (SSP). The "sdw_master_ops" structure abstracts the
 hardware details of the Master from the Bus.

 "sdw_master_port_ops" is used by Bus to setup the Port parameters of the
 Master interface Port. Master interface Port register map is not defined by
 MIPI specification, so Bus calls the "sdw_master_port_ops" callback
 function to do Port operations like "Port Prepare", "Port Transport params
 set", "Port enable and disable". The implementation of the Master driver can
 then perform hardware-specific configurations.

 Programming interfaces (SoundWire Slave Driver)
 ===============================================

 The MIPI specification requires each Slave interface to expose a unique
 48-bit identifier, stored in 6 read-only dev_id registers. This dev_id
 identifier contains vendor and part information, as well as a field enabling
 to differentiate between identical components. An additional class field is
 currently unused. Slave driver is written for a specific vendor and part
 identifier, Bus enumerates the Slave device based on these two ids.
 Slave device and driver match is done based on these two ids . Probe
 of the Slave driver is called by Bus on successful match between device and
 driver id. A parent/child relationship is enforced between Master and Slave
 devices (the logical representation is aligned with the physical
 connectivity).

 The information on Master/Slave dependencies is stored in platform data,
 board-file, ACPI or DT. The MIPI Software specification defines additional
 link_id parameters for controllers that have multiple Master interfaces. The
 dev_id registers are only unique in the scope of a link, and the link_id
 unique in the scope of a controller. Both dev_id and link_id are not
 necessarily unique at the system level but the parent/child information is
 used to avoid ambiguity.

 .. code-block:: c

 	static const struct sdw_device_id slave_id[] = {
 	        SDW_SLAVE_ENTRY(0x025d, 0x700, 0),
 	        {},
 	};
 	MODULE_DEVICE_TABLE(sdw, slave_id);

 	static struct sdw_driver slave_sdw_driver = {
 	        .driver = {
 	                   .name = "slave_xxx",
 	                   .pm = &slave_runtime_pm,
 	                   },
 		.probe = slave_sdw_probe,
 		.remove = slave_sdw_remove,
 		.ops = &slave_slave_ops,
 		.id_table = slave_id,
 	};


 For capabilities, Bus implements API to read standard Slave MIPI properties
 and also provides callback in Slave ops for Slave driver to implement own
 function that provides capabilities information. Bus needs to know a set of
 Slave capabilities to program Slave registers and to control the Bus
 reconfigurations.

 Future enhancements to be done
 ==============================

  (1) Bulk Register Access (BRA) transfers.


  (2) Multiple data lane support.

 Links
 =====

 SoundWire MIPI specification 1.1 is available at:
 https://members.mipi.org/wg/All-Members/document/70290

 SoundWire MIPI DisCo (Discovery and Configuration) specification is
 available at:
 https://www.mipi.org/specifications/mipi-disco-soundwire

 (publicly accessible with registration or directly accessible to MIPI
 members)

 MIPI Alliance Manufacturer ID Page: mid.mipi.org
	===========================
	SoundWire Subsystem Summary
	===========================

	SoundWire is a new interface ratified in 2015 by the MIPI Alliance.
	SoundWire is used for transporting data typically related to audio
	functions. SoundWire interface is optimized to integrate audio devices in
	mobile or mobile inspired systems.

	SoundWire is a 2-pin multi-drop interface with data and clock line. It
	facilitates development of low cost, efficient, high performance systems.
	Broad level key features of SoundWire interface include:

	(1) Transporting all of payload data channels, control information, and setup
	commands over a single two-pin interface.

	(2) Lower clock frequency, and hence lower power consumption, by use of DDR
	(Dual Data Rate) data transmission.

	(3) Clock scaling and optional multiple data lanes to give wide flexibility
	in data rate to match system requirements.

	(4) Device status monitoring, including interrupt-style alerts to the Master.

	The SoundWire protocol supports up to eleven Slave interfaces. All the
	interfaces share the common Bus containing data and clock line. Each of the
	Slaves can support up to 14 Data Ports. 13 Data Ports are dedicated to audio
	transport. Data Port0 is dedicated to transport of Bulk control information,
	each of the audio Data Ports (1..14) can support up to 8 Channels in
	transmit or receiving mode (typically fixed direction but configurable
	direction is enabled by the specification). Bandwidth restrictions to
	~19.2..24.576Mbits/s don't however allow for 11138 channels to be
	transmitted simultaneously.

	Below figure shows an example of connectivity between a SoundWire Master and
	two Slave devices. ::

	+---------------+ +---------------+
	\| \| Clock Signal \| \|
	\| Master \|-------+-------------------------------\| Slave \|
	\| Interface \| \| Data Signal \| Interface 1 \|
	\| \|-------\|-------+-----------------------\| \|
	+---------------+ \| \| +---------------+
	\| \|
	\| \|
	\| \|
	+--+-------+--+
	\| \|
	\| Slave \|
	\| Interface 2 \|
	\| \|
	+-------------+


	Terminology
	===========

	The MIPI SoundWire specification uses the term 'device' to refer to a Master
	or Slave interface, which of course can be confusing. In this summary and
	code we use the term interface only to refer to the hardware. We follow the
	Linux device model by mapping each Slave interface connected on the bus as a
	device managed by a specific driver. The Linux SoundWire subsystem provides
	a framework to implement a SoundWire Slave driver with an API allowing
	3rd-party vendors to enable implementation-defined functionality while
	common setup/configuration tasks are handled by the bus.

	Bus:
	Implements SoundWire Linux Bus which handles the SoundWire protocol.
	Programs all the MIPI-defined Slave registers. Represents a SoundWire
	Master. Multiple instances of Bus may be present in a system.

	Slave:
	Registers as SoundWire Slave device (Linux Device). Multiple Slave devices
	can register to a Bus instance.

	Slave driver:
	Driver controlling the Slave device. MIPI-specified registers are controlled
	directly by the Bus (and transmitted through the Master driver/interface).
	Any implementation-defined Slave register is controlled by Slave driver. In
	practice, it is expected that the Slave driver relies on regmap and does not
	request direct register access.

	Programming interfaces (SoundWire Master interface Driver)
	==========================================================

	SoundWire Bus supports programming interfaces for the SoundWire Master
	implementation and SoundWire Slave devices. All the code uses the "sdw"
	prefix commonly used by SoC designers and 3rd party vendors.

	Each of the SoundWire Master interfaces needs to be registered to the Bus.
	Bus implements API to read standard Master MIPI properties and also provides
	callback in Master ops for Master driver to implement its own functions that
	provides capabilities information. DT support is not implemented at this
	time but should be trivial to add since capabilities are enabled with the
	``device_property_`` API.

	The Master interface along with the Master interface capabilities are
	registered based on board file, DT or ACPI.

	Following is the Bus API to register the SoundWire Bus:

	.. code-block:: c

	int sdw_bus_master_add(struct sdw_bus *bus,
	struct device *parent,
	struct fwnode_handle)
	{
	sdw_master_device_add(bus, parent, fwnode);

	mutex_init(&bus->lock);
	INIT_LIST_HEAD(&bus->slaves);

	/* Check ACPI for Slave devices */
	sdw_acpi_find_slaves(bus);

	/* Check DT for Slave devices */
	sdw_of_find_slaves(bus);

	return 0;
	}

	This will initialize sdw_bus object for Master device. "sdw_master_ops" and
	"sdw_master_port_ops" callback functions are provided to the Bus.

	"sdw_master_ops" is used by Bus to control the Bus in the hardware specific
	way. It includes Bus control functions such as sending the SoundWire
	read/write messages on Bus, setting up clock frequency & Stream
	Synchronization Point (SSP). The "sdw_master_ops" structure abstracts the
	hardware details of the Master from the Bus.

	"sdw_master_port_ops" is used by Bus to setup the Port parameters of the
	Master interface Port. Master interface Port register map is not defined by
	MIPI specification, so Bus calls the "sdw_master_port_ops" callback
	function to do Port operations like "Port Prepare", "Port Transport params
	set", "Port enable and disable". The implementation of the Master driver can
	then perform hardware-specific configurations.

	Programming interfaces (SoundWire Slave Driver)
	===============================================

	The MIPI specification requires each Slave interface to expose a unique
	48-bit identifier, stored in 6 read-only dev_id registers. This dev_id
	identifier contains vendor and part information, as well as a field enabling
	to differentiate between identical components. An additional class field is
	currently unused. Slave driver is written for a specific vendor and part
	identifier, Bus enumerates the Slave device based on these two ids.
	Slave device and driver match is done based on these two ids . Probe
	of the Slave driver is called by Bus on successful match between device and
	driver id. A parent/child relationship is enforced between Master and Slave
	devices (the logical representation is aligned with the physical
	connectivity).

	The information on Master/Slave dependencies is stored in platform data,
	board-file, ACPI or DT. The MIPI Software specification defines additional
	link_id parameters for controllers that have multiple Master interfaces. The
	dev_id registers are only unique in the scope of a link, and the link_id
	unique in the scope of a controller. Both dev_id and link_id are not
	necessarily unique at the system level but the parent/child information is
	used to avoid ambiguity.

	.. code-block:: c

	static const struct sdw_device_id slave_id[] = {
	SDW_SLAVE_ENTRY(0x025d, 0x700, 0),
	{},
	};
	MODULE_DEVICE_TABLE(sdw, slave_id);

	static struct sdw_driver slave_sdw_driver = {
	.driver = {
	.name = "slave_xxx",
	.pm = &slave_runtime_pm,
	},
	.probe = slave_sdw_probe,
	.remove = slave_sdw_remove,
	.ops = &slave_slave_ops,
	.id_table = slave_id,
	};


	For capabilities, Bus implements API to read standard Slave MIPI properties
	and also provides callback in Slave ops for Slave driver to implement own
	function that provides capabilities information. Bus needs to know a set of
	Slave capabilities to program Slave registers and to control the Bus
	reconfigurations.

	Future enhancements to be done
	==============================

	(1) Bulk Register Access (BRA) transfers.


	(2) Multiple data lane support.

	Links
	=====

	SoundWire MIPI specification 1.1 is available at:
	https://members.mipi.org/wg/All-Members/document/70290

	SoundWire MIPI DisCo (Discovery and Configuration) specification is
	available at:
	https://www.mipi.org/specifications/mipi-disco-soundwire

	(publicly accessible with registration or directly accessible to MIPI
	members)

	MIPI Alliance Manufacturer ID Page: mid.mipi.org