MIPI DevCon Bangalore 2017: SoundWire Linux Subsystem: An Introduction to Protocol and Linux Subsystem
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The document provides an introduction to the MIPI SoundWire protocol and its integration with the Linux subsystem, covering basics such as device types (master and slave), bus communication, and enumeration of devices. It details technical specifications including data transfer methods, bus architecture, and device management operations within the Linux environment. Additionally, it outlines the functionalities of SoundWire drivers and the associated systems for device interaction and control.
![© 2017 MIPI Alliance, Inc.
SoundWire® Linux Bus
• The Bus is instantiated by:
– int sdw_add_bus_master(struct sdw_bus *bus);
– Master allocates sdw_bus structres
– Initialized by invoking this API
• Similarly exit is performed by:
– void sdw_delete_bus_master(struct sdw_bus
*bus);
12
Intel Corp
struct sdw_bus {
struct device *dev;
bool acpi_enabled;
unsigned int link_id;
struct list_head slaves;
bool assigned[SDW_MAX_DEVICES + 1];
struct mutex bus_lock;
struct mutex msg_lock;
const struct sdw_bus_ops *bus_ops;
const struct sdw_master_ops *ops;
const struct sdw_master_port_ops *port_ops;
struct sdw_bus_params params;
struct sdw_master_prop prop;
struct sdw_master_sysfs *sysfs;
struct sdw_defer defer_msg;
enum sdw_bus_ops_impl impl;
unsigned int clk_stop_timeout;
};](https://image.slidesharecdn.com/bangalore-intel-soundwire-linux-subsystem-171110204700/85/MIPI-DevCon-Bangalore-2017-SoundWire-Linux-Subsystem-An-Introduction-to-Protocol-and-Linux-Subsystem-12-320.jpg)
MIPI DevCon Bangalore 2017: SoundWire Linux Subsystem: An Introduction to Protocol and Linux Subsystem
- 1. Vinod Koul, Sanyog Kale Intel Corp MIPI SoundWire® Linux Subsystem: An introduction to Protocol and Linux Subsystem
- 2. © 2017 MIPI Alliance, Inc. Agenda • MIPI SoundWire® Basics • Linux Subsystem • SoundWire Linux Bus • SoundWire Master • SoundWire Slave 2 Intel Corp
- 3. © 2017 MIPI Alliance, Inc. SoundWire® PHY • Support one of 1.2 or 1.8 V • Clock up to 12.288MHz • Dual data rate • Modified NRZI encoding – Logic 0: physical signal inverted from value in preceding bitSlot – Logic 1: no change in physical signal, level maintained by bus-keeper • TDM – Each device ‘owns’ bit slot • Data – PCM – PDM – Bulk Transfers • Bulk Register Access (BRA) • Bulk Transfer Protocol (BTP) 3 Intel Corp
- 4. © 2017 MIPI Alliance, Inc. Device Types • Master – Provides Clock and Sync pattern on data line – Bus management, bit allocation • Slave – Audio peripheral (MIC, Codec, Amps) – 1 to 11 Slaves connected, Multi-drop bus – In band Interrupt, System wake • Monitor – Test equipment, in snoop analyze mode – Temporarily take over bus, issue Read/Write commands 4 Intel Corp
- 8. © 2017 MIPI Alliance, Inc. Enumeration • Register DevId 0-5, 48-bit unique value – ManufacturerID, PartID – Class (not defined yet) – SoundWire spec version – UniqueID • Slave reports present on Dev Num 0 • Master reads DevId 0-5 • Assigns Dev Num X (1..11) • Slave reports present on Dev Num X 8 Intel Corp
- 9. © 2017 MIPI Alliance, Inc. SoundWire® DisCo℠ • MIPI Discovery and Configuration (DisCo℠) mechanism • MIPI adopted Spec • Optional, but values mandatory for Software • Implemented as ACPI _DSD methods • Describes SoundWire Master properties and Slave properties 9 Intel Corp
- 12. © 2017 MIPI Alliance, Inc. SoundWire® Linux Bus • The Bus is instantiated by: – int sdw_add_bus_master(struct sdw_bus *bus); – Master allocates sdw_bus structres – Initialized by invoking this API • Similarly exit is performed by: – void sdw_delete_bus_master(struct sdw_bus *bus); 12 Intel Corp struct sdw_bus { struct device *dev; bool acpi_enabled; unsigned int link_id; struct list_head slaves; bool assigned[SDW_MAX_DEVICES + 1]; struct mutex bus_lock; struct mutex msg_lock; const struct sdw_bus_ops *bus_ops; const struct sdw_master_ops *ops; const struct sdw_master_port_ops *port_ops; struct sdw_bus_params params; struct sdw_master_prop prop; struct sdw_master_sysfs *sysfs; struct sdw_defer defer_msg; enum sdw_bus_ops_impl impl; unsigned int clk_stop_timeout; };
- 13. © 2017 MIPI Alliance, Inc. IO • Slaves typically have Audio function • Need IO access for implementation defined registers – Support read/write along with ‘n’ consecutive read/write 13 Intel Corp int sdw_read(struct sdw_slave *slave, u32 addr); int sdw_write(struct sdw_slave *slave, u32 addr, u8 value); int sdw_nread(struct sdw_slave *slave, u32 addr, size_t count, u8 *val); int sdw_nwrite(struct sdw_slave *slave, u32 addr, size_t count, u8 *val);
- 14. © 2017 MIPI Alliance, Inc. SoundWire® Enumeration • SoundWire protocol enumerable but not discoverable • Slaves maybe powered off on boot – Protocol enumeration doesn’t work then • Implementation (ACPI/DT) based – Create SoundWire Slaves based on firmware description – Mark Slaves PRESENT when they show up 14 Intel Corp
- 15. © 2017 MIPI Alliance, Inc. SoundWire® Linux Slave • Slave Driver registers Slave to Bus – int sdw_register_driver(struct sdw_driver *drv); – void sdw_unregister_driver(struct sdw_driver *drv); • Probed when device found in firmware description – Matching uses only Manufacturer ID, Part ID – Instance not used, load same driver for different instances 15 Intel Corp
- 16. © 2017 MIPI Alliance, Inc. SoundWire® Slave Driver • Typical Linux subsystem driver • Provides probe, remove, shutdown methods • ID table for SDW IDs • Ops for Slave driver callbacks 16 Intel Corp struct sdw_driver { const char *name; int (*probe)(struct sdw_slave *sdw, const struct sdw_device_id *id); int (*remove)(struct sdw_slave *sdw); void (*shutdown)(struct sdw_slave *sdw); const struct sdw_device_id *id_table; const struct sdw_slave_ops *ops; struct device_driver driver; }; struct sdw_device_id { __u16 mfg_id; __u16 part_id; __u8 class_id; kernel_ulong_t driver_data; };
- 18. © 2017 MIPI Alliance, Inc. Links • SoundWire® Brief http://www.aes.org/e-lib/browse.cfm?elib=17407 • SoundWire® Spec v1.1 https://members.mipi.org/wg/All- Members/document/70290 • SoundWire® DisCo℠ Spec v1.0 https://members.mipi.org/wg/All- Members/document/71260 • SoundWire® Source Tree https://git.kernel.org/pub/scm/linux/kernel/git/vkoul/soundwire.git/ 18 Intel Corp
- 20. © 2017 MIPI Alliance, Inc. Slaves • Status – Not Attached (Not present/operational) – Attached (synchronized w/ Master and able to handle commands) – Alert (synchronized, at least one Interrupt condition raised) • Up to 11 Slaves per link, each w/ Unique Device Number – Dev Num 0: Attached, but not enumerated – Dev Num 1 -11: Enumerated Device – Dev Num 12-13: Group – Dev Num 14: Reserved for Master – Dev Num 15: Broadcast • Data Ports – DP0: Bulk command protocol (BRA, BTP) – DP1-DP14: Data ports (for audio streaming) – DP15: Alias port (program all ports with single command) 20 Intel Corp
- 21. © 2017 MIPI Alliance, Inc. Frame • Serial transmission but frame defined by 2D pattern (MaxRow, MaxCol) • Command/Control: – First 48 Rows of Col0 • PCM – Can use multiple columns/multiple rows • Low latency streams (1-bit PDM): – Samples evenly distributed in time – ‘vertical stripes’ in bit allocation – No conflicts with command/control or PCM 21 Intel Corp
- 22. © 2017 MIPI Alliance, Inc. Master Operations • Spec doesn’t define Master implementation • Bus provides ops for Master Driver, Mandatory – DisCo property read – Transfer messages (IO) – Register Bank Switches • Optional – Setting SSP interval – Bus Parameters computation 22 Intel Corp struct sdw_master_ops { int (*read_prop)(struct sdw_bus *bus); enum sdw_command_response (*xfer_msg) (struct sdw_bus *bus, struct sdw_msg *msg, int page); enum sdw_command_response (*xfer_msg_defer) (struct sdw_bus *bus, struct sdw_msg *msg, int page, struct sdw_defer *defer); enum sdw_command_response (*reset_page_addr) (struct sdw_bus *bus, unsigned int dev_num); int (*set_ssp_interval)(struct sdw_bus *bus, unsigned int ssp_interval, unsigned int bank); int (*set_bus_conf)(struct sdw_bus *bus, struct sdw_bus_conf *conf); int (*pre_bank_switch)(struct sdw_bus *bus); int (*post_bank_switch)(struct sdw_bus *bus); };
- 23. © 2017 MIPI Alliance, Inc. Slave Driver Ops • DisCo property read • Interrupt update (implementation defined interrupts) • Clock stop query and apply • Bus configuration change update • Data port prepare (pre/post) 23 Intel Corp struct sdw_slave_ops { int (*read_prop)(struct sdw_slave *sdw); int (*interrupt_callback)(struct sdw_slave *slave, struct sdw_slave_intr_status *status); int (*update_status)(struct sdw_slave *slave, enum sdw_slave_status status); int (*get_clk_stop_mode)(struct sdw_slave *slave); int (*clk_stop)(struct sdw_slave *slave, enum sdw_clk_stop_mode mode, enum sdw_clok_stop_type type); int (*pre_bus_config)(struct sdw_slave *slave, struct sdw_bus_conf *conf); int (*port_prep)(struct sdw_slave *slave, struct sdw_prepare_ch *prepare_ch, enum sdw_port_prep_ops pre_ops); };
- 24. © 2017 MIPI Alliance, Inc. Frame Shape • Columns: 2-4-6-8-10-12-14-16 • Rows: 48 to 256, not all combinations are valid • Frame shape determined by – Bus clock – Frame rate typically 8-48 kHz – Audio sample rate – Oversampling ratio for PDM • Slaves are required to handle pairwise combinations of Rows, Cols • Master will typically only use few combinations based on 2^n factors 24 Intel Corp