Linux カーネル SLIMbus サポート

Overview

What is SLIMbus?

SLIMbus (Serial Low Power Interchip Media Bus) is a specification developed by MIPI (Mobile Industry Processor Interface) alliance. The bus uses master/slave configuration, and is a 2-wire multi-drop implementation (clock, and data).

Currently, SLIMbus is used to interface between application processors of SoCs (System-on-Chip) and peripheral components (typically codec). SLIMbus uses Time-Division-Multiplexing to accommodate multiple data channels, and a control channel.

The control channel is used for various control functions such as bus management, configuration and status updates. These messages can be unicast (e.g. reading/writing device specific values), or multicast (e.g. data channel reconfiguration sequence is a broadcast message announced to all devices)

A data channel is used for data-transfer between 2 SLIMbus devices. Data channel uses dedicated ports on the device.

Hardware description:

SLIMbus specification has different types of device classifications based on their capabilities. A manager device is responsible for enumeration, configuration, and dynamic channel allocation. Every bus has 1 active manager.

A generic device is a device providing application functionality (e.g. codec).

Framer device is responsible for clocking the bus, and transmitting frame-sync and framing information on the bus.

Each SLIMbus component has an interface device for monitoring physical layer.

Typically each SoC contains SLIMbus component having 1 manager, 1 framer device, 1 generic device (for data channel support), and 1 interface device. External peripheral SLIMbus component usually has 1 generic device (for functionality/data channel support), and an associated interface device. The generic device's registers are mapped as 'value elements' so that they can be written/read using SLIMbus control channel exchanging control/status type of information. In case there are multiple framer devices on the same bus, manager device is responsible to select the active-framer for clocking the bus.

Per specification, SLIMbus uses "clock gears" to do power management based on current frequency and bandwidth requirements. There are 10 clock gears and each gear changes the SLIMbus frequency to be twice its previous gear.

Each device has a 6-byte enumeration-address and the manager assigns every device with a 1-byte logical address after the devices report presence on the bus.

Software description:

There are 2 types of SLIMbus drivers:

slim_controller represents a 'controller' for SLIMbus. This driver should implement duties needed by the SoC (manager device, associated interface device for monitoring the layers and reporting errors, default framer device).

slim_device represents the 'generic device/component' for SLIMbus, and a slim_driver should implement driver for that slim_device.

Device notifications to the driver:

Since SLIMbus devices have mechanisms for reporting their presence, the framework allows drivers to bind when corresponding devices report their presence on the bus. However, it is possible that the driver needs to be probed first so that it can enable corresponding SLIMbus device (e.g. power it up and/or take it out of reset). To support that behavior, the framework allows drivers to probe first as well (e.g. using standard DeviceTree compatibility field). This creates the necessity for the driver to know when the device is functional (i.e. reported present). device_up callback is used for that reason when the device reports present and is assigned a logical address by the controller.

Similarly, SLIMbus devices 'report absent' when they go down. A 'device_down' callback notifies the driver when the device reports absent and its logical address assignment is invalidated by the controller.

Another notification "boot_device" is used to notify the slim_driver when controller resets the bus. This notification allows the driver to take necessary steps to boot the device so that it's functional after the bus has been reset.

Driver and Controller APIs:

struct slim_eaddr

Enumeration address for a SLIMbus device

Definition

struct slim_eaddr {
  u8 instance;
  u8 dev_index;
  u16 prod_code;
  u16 manf_id;
};

Members

instance
Instance value
dev_index
Device index
prod_code
Product code
manf_id
Manufacturer Id for the device
enum slim_device_status

slim device status

Constants

SLIM_DEVICE_STATUS_DOWN
Slim device is absent or not reported yet.
SLIM_DEVICE_STATUS_UP
Slim device is announced on the bus.
SLIM_DEVICE_STATUS_RESERVED
Reserved for future use.
struct slim_device

Slim device handle.

Definition

struct slim_device {
  struct device           dev;
  struct slim_eaddr       e_addr;
  struct slim_controller  *ctrl;
  enum slim_device_status status;
  u8 laddr;
  bool is_laddr_valid;
  struct list_head        stream_list;
  spinlock_t stream_list_lock;
};

Members

dev
Driver model representation of the device.
e_addr
Enumeration address of this device.
ctrl
slim controller instance.
status
slim device status
laddr
1-byte Logical address of this device.
is_laddr_valid
indicates if the laddr is valid or not
stream_list
List of streams on this device
stream_list_lock
lock to protect the stream list

Description

This is the client/device handle returned when a SLIMbus device is registered with a controller. Pointer to this structure is used by client-driver as a handle.

struct slim_driver

SLIMbus 'generic device' (slave) device driver (similar to 'spi_device' on SPI)

Definition

struct slim_driver {
  int (*probe)(struct slim_device *sl);
  void (*remove)(struct slim_device *sl);
  void (*shutdown)(struct slim_device *sl);
  int (*device_status)(struct slim_device *sl, enum slim_device_status s);
  struct device_driver            driver;
  const struct slim_device_id     *id_table;
};

Members

probe
Binds this driver to a SLIMbus device.
remove
Unbinds this driver from the SLIMbus device.
shutdown
Standard shutdown callback used during powerdown/halt.
device_status
This callback is called when - The device reports present and gets a laddr assigned - The device reports absent, or the bus goes down.
driver
SLIMbus device drivers should initialize name and owner field of this structure
id_table
List of SLIMbus devices supported by this driver
struct slim_val_inf

Slimbus value or information element

Definition

struct slim_val_inf {
  u16 start_offset;
  u8 num_bytes;
  u8 *rbuf;
  const u8                *wbuf;
  struct completion      *comp;
};

Members

start_offset
Specifies starting offset in information/value element map
num_bytes
upto 16. This ensures that the message will fit the slicesize per SLIMbus spec
rbuf
buffer to read the values
wbuf
buffer to write
comp
completion for asynchronous operations, valid only if TID is required for transaction, like REQUEST operations. Rest of the transactions are synchronous anyway.
struct slim_stream_config

SLIMbus stream configuration Configuring a stream is done at hw_params or prepare call from audio drivers where they have all the required information regarding rate, number of channels and so on. There is a 1:1 mapping of channel and ports.

Definition

struct slim_stream_config {
  unsigned int rate;
  unsigned int bps;
  unsigned int ch_count;
  unsigned int *chs;
  unsigned long port_mask;
  int direction;
};

Members

rate
data rate
bps
bits per data sample
ch_count
number of channels
chs
pointer to list of channel numbers
port_mask
port mask of ports to use for this stream
direction
direction of the stream, SNDRV_PCM_STREAM_PLAYBACK or SNDRV_PCM_STREAM_CAPTURE.
module_slim_driver(__slim_driver)

Helper macro for registering a SLIMbus driver

Parameters

__slim_driver
slimbus_driver struct

Description

Helper macro for SLIMbus drivers which do not do anything special in module init/exit. This eliminates a lot of boilerplate. Each module may only use this macro once, and calling it replaces module_init() and module_exit()

struct slim_framer

Represents SLIMbus framer. Every controller may have multiple framers. There is 1 active framer device responsible for clocking the bus. Manager is responsible for framer hand-over.

Definition

struct slim_framer {
  struct device           dev;
  struct slim_eaddr       e_addr;
  int rootfreq;
  int superfreq;
};

Members

dev
Driver model representation of the device.
e_addr
Enumeration address of the framer.
rootfreq
Root Frequency at which the framer can run. This is maximum frequency ('clock gear 10') at which the bus can operate.
superfreq
Superframes per root frequency. Every frame is 6144 bits.
struct slim_msg_txn

Message to be sent by the controller. This structure has packet header, payload and buffer to be filled (if any)

Definition

struct slim_msg_txn {
  u8 rl;
  u8 mt;
  u8 mc;
  u8 dt;
  u16 ec;
  u8 tid;
  u8 la;
  struct slim_val_inf     *msg;
  struct completion      *comp;
};

Members

rl
Header field. remaining length.
mt
Header field. Message type.
mc
Header field. LSB is message code for type mt.
dt
Header field. Destination type.
ec
Element code. Used for elemental access APIs.
tid
Transaction ID. Used for messages expecting response. (relevant for message-codes involving read operation)
la
Logical address of the device this message is going to. (Not used when destination type is broadcast.)
msg
Elemental access message to be read/written
comp
completion if read/write is synchronous, used internally for tid based transactions.
enum slim_clk_state

Constants

SLIM_CLK_ACTIVE
SLIMbus clock is active
SLIM_CLK_ENTERING_PAUSE
SLIMbus clock pause sequence is being sent on the bus. If this succeeds, state changes to SLIM_CLK_PAUSED. If the transition fails, state changes back to SLIM_CLK_ACTIVE
SLIM_CLK_PAUSED
SLIMbus controller clock has paused.

Description

maintaining current clock state.
struct slim_sched

Definition

struct slim_sched {
  enum slim_clk_state     clk_state;
  struct completion       pause_comp;
  struct mutex            m_reconf;
};

Members

clk_state
Controller's clock state from enum slim_clk_state
pause_comp
Signals completion of clock pause sequence. This is useful when client tries to call SLIMbus transaction when controller is entering clock pause.
m_reconf
This mutex is held until current reconfiguration (data channel scheduling, message bandwidth reservation) is done. Message APIs can use the bus concurrently when this mutex is held since elemental access messages can be sent on the bus when reconfiguration is in progress.
enum slim_port_direction

Constants

SLIM_PORT_SINK
SLIMbus port is a sink
SLIM_PORT_SOURCE
SLIMbus port is a source
enum slim_port_state

Constants

SLIM_PORT_DISCONNECTED
SLIMbus port is disconnected entered from Unconfigure/configured state after DISCONNECT_PORT or REMOVE_CHANNEL core command
SLIM_PORT_UNCONFIGURED
SLIMbus port is in unconfigured state. entered from disconnect state after CONNECT_SOURCE/SINK core command
SLIM_PORT_CONFIGURED
SLIMbus port is in configured state. entered from unconfigured state after DEFINE_CHANNEL, DEFINE_CONTENT and ACTIVATE_CHANNEL core commands. Ready for data transmission.

Description

according to SLIMbus Spec 2.0
enum slim_channel_state

Constants

SLIM_CH_STATE_DISCONNECTED
SLIMbus channel is disconnected
SLIM_CH_STATE_ALLOCATED
SLIMbus channel is allocated
SLIM_CH_STATE_ASSOCIATED
SLIMbus channel is associated with port
SLIM_CH_STATE_DEFINED
SLIMbus channel parameters are defined
SLIM_CH_STATE_CONTENT_DEFINED
SLIMbus channel content is defined
SLIM_CH_STATE_ACTIVE
SLIMbus channel is active and ready for data
SLIM_CH_STATE_REMOVED
SLIMbus channel is inactive and removed
enum slim_ch_data_fmt

Constants

SLIM_CH_DATA_FMT_NOT_DEFINED
Undefined
SLIM_CH_DATA_FMT_LPCM_AUDIO
LPCM audio
SLIM_CH_DATA_FMT_IEC61937_COMP_AUDIO
IEC61937 Compressed audio
SLIM_CH_DATA_FMT_PACKED_PDM_AUDIO
Packed PDM audio

Description

Table 60 of SLIMbus Spec 1.01.01
enum slim_ch_aux_bit_fmt

Constants

SLIM_CH_AUX_FMT_NOT_APPLICABLE
Undefined
SLIM_CH_AUX_FMT_ZCUV_TUNNEL_IEC60958
ZCUV for tunneling IEC60958
SLIM_CH_AUX_FMT_USER_DEFINED
User defined

Description

Table 63 of SLIMbus Spec 2.0
struct slim_channel

SLIMbus channel, used for state machine

Definition

struct slim_channel {
  int id;
  int prrate;
  int seg_dist;
  enum slim_ch_data_fmt data_fmt;
  enum slim_ch_aux_bit_fmt aux_fmt;
  enum slim_channel_state state;
};

Members

id
ID of channel
prrate
Presense rate of channel from Table 66 of SLIMbus 2.0 Specs
seg_dist
segment distribution code from Table 20 of SLIMbus 2.0 Specs
data_fmt
Data format of channel.
aux_fmt
Aux format for this channel.
state
channel state machine
struct slim_port

SLIMbus port

Definition

struct slim_port {
  int id;
  enum slim_port_direction direction;
  enum slim_port_state state;
  struct slim_channel ch;
};

Members

id
Port id
direction
Port direction, Source or Sink.
state
state machine of port.
ch
channel associated with this port.
enum slim_transport_protocol

Constants

SLIM_PROTO_ISO
Isochronous Protocol, no flow control as data rate match channel rate flow control embedded in the data.
SLIM_PROTO_PUSH
Pushed Protocol, includes flow control, Used to carry data whose rate is equal to, or lower than the channel rate.
SLIM_PROTO_PULL
Pulled Protocol, similar usage as pushed protocol but pull is a unicast.
SLIM_PROTO_LOCKED
Locked Protocol
SLIM_PROTO_ASYNC_SMPLX
Asynchronous Protocol-Simplex
SLIM_PROTO_ASYNC_HALF_DUP
Asynchronous Protocol-Half-duplex
SLIM_PROTO_EXT_SMPLX
Extended Asynchronous Protocol-Simplex
SLIM_PROTO_EXT_HALF_DUP
Extended Asynchronous Protocol-Half-duplex

Description

Table 47 of SLIMbus 2.0 specs.
struct slim_stream_runtime

SLIMbus stream runtime instance

Definition

struct slim_stream_runtime {
  const char *name;
  struct slim_device *dev;
  int direction;
  enum slim_transport_protocol prot;
  unsigned int rate;
  unsigned int bps;
  unsigned int ratem;
  int num_ports;
  struct slim_port *ports;
  struct list_head node;
};

Members

name
Name of the stream
dev
SLIM Device instance associated with this stream
direction
direction of stream
prot
Transport protocol used in this stream
rate
Data rate of samples *
bps
bits per sample
ratem
rate multipler which is super frame rate/data rate
num_ports
number of ports
ports
pointer to instance of ports
node
list head for stream associated with slim device.
struct slim_controller

Controls every instance of SLIMbus (similar to 'master' on SPI)

Definition

struct slim_controller {
  struct device           *dev;
  unsigned int            id;
  char name[SLIMBUS_NAME_SIZE];
  int min_cg;
  int max_cg;
  int clkgear;
  struct ida              laddr_ida;
  struct slim_framer      *a_framer;
  struct mutex            lock;
  struct list_head        devices;
  struct idr              tid_idr;
  spinlock_t txn_lock;
  struct slim_sched       sched;
  int (*xfer_msg)(struct slim_controller *ctrl, struct slim_msg_txn *tx);
  int (*set_laddr)(struct slim_controller *ctrl, struct slim_eaddr *ea, u8 laddr);
  int (*get_laddr)(struct slim_controller *ctrl, struct slim_eaddr *ea, u8 *laddr);
  int (*enable_stream)(struct slim_stream_runtime *rt);
  int (*disable_stream)(struct slim_stream_runtime *rt);
  int (*wakeup)(struct slim_controller *ctrl);
};

Members

dev
Device interface to this driver
id
Board-specific number identifier for this controller/bus
name
Name for this controller
min_cg
Minimum clock gear supported by this controller (default value: 1)
max_cg
Maximum clock gear supported by this controller (default value: 10)
clkgear
Current clock gear in which this bus is running
laddr_ida
logical address id allocator
a_framer
Active framer which is clocking the bus managed by this controller
lock
Mutex protecting controller data structures
devices
Slim device list
tid_idr
tid id allocator
txn_lock
Lock to protect table of transactions
sched
scheduler structure used by the controller
xfer_msg
Transfer a message on this controller (this can be a broadcast control/status message like data channel setup, or a unicast message like value element read/write.
set_laddr
Setup logical address at laddr for the slave with elemental address e_addr. Drivers implementing controller will be expected to send unicast message to this device with its logical address.
get_laddr
It is possible that controller needs to set fixed logical address table and get_laddr can be used in that case so that controller can do this assignment. Use case is when the master is on the remote processor side, who is resposible for allocating laddr.
enable_stream
This function pointer implements controller-specific procedure to enable a stream.
disable_stream
This function pointer implements controller-specific procedure to disable stream.
wakeup
This function pointer implements controller-specific procedure to wake it up from clock-pause. Framework will call this to bring the controller out of clock pause.

Description

'Manager device' is responsible for device management, bandwidth allocation, channel setup, and port associations per channel. Device management means Logical address assignment/removal based on enumeration (report-present, report-absent) of a device. Bandwidth allocation is done dynamically by the manager based on active channels on the bus, message-bandwidth requests made by SLIMbus devices. Based on current bandwidth usage, manager chooses a frequency to run the bus at (in steps of 'clock-gear', 1 through 10, each clock gear representing twice the frequency than the previous gear). Manager is also responsible for entering (and exiting) low-power-mode (known as 'clock pause'). Manager can do handover of framer if there are multiple framers on the bus and a certain usecase warrants using certain framer to avoid keeping previous framer being powered-on.

Controller here performs duties of the manager device, and 'interface device'. Interface device is responsible for monitoring the bus and reporting information such as loss-of-synchronization, data slot-collision.

int slim_unregister_controller(struct slim_controller * ctrl)

Controller tear-down.

Parameters

struct slim_controller * ctrl
Controller to tear-down.
void slim_report_absent(struct slim_device * sbdev)

Controller calls this function when a device reports absent, OR when the device cannot be communicated with

Parameters

struct slim_device * sbdev
Device that cannot be reached, or sent report absent
struct slim_device * slim_get_device(struct slim_controller * ctrl, struct slim_eaddr * e_addr)

get handle to a device.

Parameters

struct slim_controller * ctrl
Controller on which this device will be added/queried
struct slim_eaddr * e_addr
Enumeration address of the device to be queried

Return

pointer to a device if it has already reported. Creates a new device and returns pointer to it if the device has not yet enumerated.

struct slim_device * of_slim_get_device(struct slim_controller * ctrl, struct device_node * np)

get handle to a device using dt node.

Parameters

struct slim_controller * ctrl
Controller on which this device will be added/queried
struct device_node * np
node pointer to device

Return

pointer to a device if it has already reported. Creates a new device and returns pointer to it if the device has not yet enumerated.

int slim_device_report_present(struct slim_controller * ctrl, struct slim_eaddr * e_addr, u8 * laddr)

Report enumerated device.

Parameters

struct slim_controller * ctrl
Controller with which device is enumerated.
struct slim_eaddr * e_addr
Enumeration address of the device.
u8 * laddr
Return logical address (if valid flag is false)

Description

Called by controller in response to REPORT_PRESENT. Framework will assign a logical address to this enumeration address. Function returns -EXFULL to indicate that all logical addresses are already taken.

int slim_get_logical_addr(struct slim_device * sbdev)

get/allocate logical address of a SLIMbus device.

Parameters

struct slim_device * sbdev
client handle requesting the address.

Return

zero if a logical address is valid or a new logical address has been assigned. error code in case of error.

Clock-pause:

SLIMbus mandates that a reconfiguration sequence (known as clock-pause) be broadcast to all active devices on the bus before the bus can enter low-power mode. Controller uses this sequence when it decides to enter low-power mode so that corresponding clocks and/or power-rails can be turned off to save power. Clock-pause is exited by waking up framer device (if controller driver initiates exiting low power mode), or by toggling the data line (if a slave device wants to initiate it).

Clock-pause APIs:

int slim_ctrl_clk_pause(struct slim_controller * ctrl, bool wakeup, u8 restart)

Called by slimbus controller to enter/exit 'clock pause'

Parameters

struct slim_controller * ctrl
controller requesting bus to be paused or woken up
bool wakeup
Wakeup this controller from clock pause.
u8 restart
Restart time value per spec used for clock pause. This value isn't used when controller is to be woken up.

Description

Slimbus specification needs this sequence to turn-off clocks for the bus. The sequence involves sending 3 broadcast messages (reconfiguration sequence) to inform all devices on the bus. To exit clock-pause, controller typically wakes up active framer device. This API executes clock pause reconfiguration sequence if wakeup is false. If wakeup is true, controller's wakeup is called. For entering clock-pause, -EBUSY is returned if a message txn in pending.

Messaging:

The framework supports regmap and read/write apis to exchange control-information with a SLIMbus device. APIs can be synchronous or asynchronous. The header file <linux/slimbus.h> has more documentation about messaging APIs.

Messaging APIs:

void slim_msg_response(struct slim_controller * ctrl, u8 * reply, u8 tid, u8 len)

Deliver Message response received from a device to the framework.

Parameters

struct slim_controller * ctrl
Controller handle
u8 * reply
Reply received from the device
u8 tid
Transaction ID received with which framework can associate reply.
u8 len
Length of the reply

Description

Called by controller to inform framework about the response received. This helps in making the API asynchronous, and controller-driver doesn't need to manage 1 more table other than the one managed by framework mapping TID with buffers

int slim_alloc_txn_tid(struct slim_controller * ctrl, struct slim_msg_txn * txn)

Allocate a tid to txn

Parameters

struct slim_controller * ctrl
Controller handle
struct slim_msg_txn * txn
transaction to be allocated with tid.

Return

zero on success with valid txn->tid and error code on failures.

void slim_free_txn_tid(struct slim_controller * ctrl, struct slim_msg_txn * txn)

Freee tid of txn

Parameters

struct slim_controller * ctrl
Controller handle
struct slim_msg_txn * txn
transaction whose tid should be freed
int slim_do_transfer(struct slim_controller * ctrl, struct slim_msg_txn * txn)

Process a SLIMbus-messaging transaction

Parameters

struct slim_controller * ctrl
Controller handle
struct slim_msg_txn * txn
Transaction to be sent over SLIMbus

Description

Called by controller to transmit messaging transactions not dealing with Interface/Value elements. (e.g. transmittting a message to assign logical address to a slave device

Return

-ETIMEDOUT: If transmission of this message timed out
(e.g. due to bus lines not being clocked or driven by controller)
int slim_xfer_msg(struct slim_device * sbdev, struct slim_val_inf * msg, u8 mc)

Transfer a value info message on slim device

Parameters

struct slim_device * sbdev
slim device to which this msg has to be transfered
struct slim_val_inf * msg
value info message pointer
u8 mc
message code of the message

Description

Called by drivers which want to transfer a vlaue or info elements.

Return

-ETIMEDOUT: If transmission of this message timed out

int slim_read(struct slim_device * sdev, u32 addr, size_t count, u8 * val)

Read SLIMbus value element

Parameters

struct slim_device * sdev
client handle.
u32 addr
address of value element to read.
size_t count
number of bytes to read. Maximum bytes allowed are 16.
u8 * val
will return what the value element value was

Return

-EINVAL for Invalid parameters, -ETIMEDOUT If transmission of this message timed out (e.g. due to bus lines not being clocked or driven by controller)

int slim_readb(struct slim_device * sdev, u32 addr)

Read byte from SLIMbus value element

Parameters

struct slim_device * sdev
client handle.
u32 addr
address in the value element to read.

Return

byte value of value element.

int slim_write(struct slim_device * sdev, u32 addr, size_t count, u8 * val)

Write SLIMbus value element

Parameters

struct slim_device * sdev
client handle.
u32 addr
address in the value element to write.
size_t count
number of bytes to write. Maximum bytes allowed are 16.
u8 * val
value to write to value element

Return

-EINVAL for Invalid parameters, -ETIMEDOUT If transmission of this message timed out (e.g. due to bus lines not being clocked or driven by controller)

int slim_writeb(struct slim_device * sdev, u32 addr, u8 value)

Write byte to SLIMbus value element

Parameters

struct slim_device * sdev
client handle.
u32 addr
address of value element to write.
u8 value
value to write to value element

Return

-EINVAL for Invalid parameters, -ETIMEDOUT If transmission of this message timed out (e.g. due to bus lines not being clocked or driven by controller)

Streaming APIs: