High Speed Synchronous Serial Interface (HSI)¶
Introduction¶
High Speed Syncronous Interface (HSI) is a fullduplex, low latency protocol, that is optimized for die-level interconnect between an Application Processor and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and implemented by multiple vendors since then.
The HSI interface supports full duplex communication over multiple channels (typically 8) and is capable of reaching speeds up to 200 Mbit/s.
The serial protocol uses two signals, DATA and FLAG as combined data and clock signals and an additional READY signal for flow control. An additional WAKE signal can be used to wakeup the chips from standby modes. The signals are commonly prefixed by AC for signals going from the application die to the cellular die and CA for signals going the other way around.
+------------+ +---------------+
| Cellular | | Application |
| Die | | Die |
| | - - - - - - CAWAKE - - - - - - >| |
| T|------------ CADATA ------------>|R |
| X|------------ CAFLAG ------------>|X |
| |<----------- ACREADY ------------| |
| | | |
| | | |
| |< - - - - - ACWAKE - - - - - - -| |
| R|<----------- ACDATA -------------|T |
| X|<----------- ACFLAG -------------|X |
| |------------ CAREADY ----------->| |
| | | |
| | | |
+------------+ +---------------+
HSI Subsystem in Linux¶
In the Linux kernel the hsi subsystem is supposed to be used for HSI devices. The hsi subsystem contains drivers for hsi controllers including support for multi-port controllers and provides a generic API for using the HSI ports.
It also contains HSI client drivers, which make use of the generic API to implement a protocol used on the HSI interface. These client drivers can use an arbitrary number of channels.
hsi-char Device¶
Each port automatically registers a generic client driver called hsi_char, which provides a charecter device for userspace representing the HSI port. It can be used to communicate via HSI from userspace. Userspace may configure the hsi_char device using the following ioctl commands:
- HSC_RESET
- flush the HSI port
- HSC_SET_PM
- enable or disable the client.
- HSC_SEND_BREAK
- send break
- HSC_SET_RX
- set RX configuration
- HSC_GET_RX
- get RX configuration
- HSC_SET_TX
- set TX configuration
- HSC_GET_TX
- get TX configuration
The kernel HSI API¶
-
struct
hsi_channel¶ channel resource used by the hsi clients
Definition
struct hsi_channel {
unsigned int id;
const char *name;
};
Members
id- Channel number
name- Channel name
-
struct
hsi_config¶ Configuration for RX/TX HSI modules
Definition
struct hsi_config {
unsigned int mode;
struct hsi_channel *channels;
unsigned int num_channels;
unsigned int num_hw_channels;
unsigned int speed;
union {
unsigned int flow;
unsigned int arb_mode;
};
};
Members
mode- Bit transmission mode (STREAM or FRAME)
channels- Channel resources used by the client
num_channels- Number of channel resources
num_hw_channels- Number of channels the transceiver is configured for [1..16]
speed- Max bit transmission speed (Kbit/s)
{unnamed_union}- anonymous
flow- RX flow type (SYNCHRONIZED or PIPELINE)
arb_mode- Arbitration mode for TX frame (Round robin, priority)
-
struct
hsi_board_info¶ HSI client board info
Definition
struct hsi_board_info {
const char *name;
unsigned int hsi_id;
unsigned int port;
struct hsi_config tx_cfg;
struct hsi_config rx_cfg;
void *platform_data;
struct dev_archdata *archdata;
};
Members
name- Name for the HSI device
hsi_id- HSI controller id where the client sits
port- Port number in the controller where the client sits
tx_cfg- HSI TX configuration
rx_cfg- HSI RX configuration
platform_data- Platform related data
archdata- Architecture-dependent device data
-
struct
hsi_client¶ HSI client attached to an HSI port
Definition
struct hsi_client {
struct device device;
struct hsi_config tx_cfg;
struct hsi_config rx_cfg;
};
Members
device- Driver model representation of the device
tx_cfg- HSI TX configuration
rx_cfg- HSI RX configuration
-
struct
hsi_client_driver¶ Driver associated to an HSI client
Definition
struct hsi_client_driver {
struct device_driver driver;
};
Members
driver- Driver model representation of the driver
-
struct
hsi_msg¶ HSI message descriptor
Definition
struct hsi_msg {
struct list_head link;
struct hsi_client *cl;
struct sg_table sgt;
void *context;
void (*complete)(struct hsi_msg *msg);
void (*destructor)(struct hsi_msg *msg);
int status;
unsigned int actual_len;
unsigned int channel;
unsigned int ttype:1;
unsigned int break_frame:1;
};
Members
link- Free to use by the current descriptor owner
cl- HSI device client that issues the transfer
sgt- Head of the scatterlist array
context- Client context data associated to the transfer
complete- Transfer completion callback
destructor- Destructor to free resources when flushing
status- Status of the transfer when completed
actual_len- Actual length of data transferred on completion
channel- Channel were to TX/RX the message
ttype- Transfer type (TX if set, RX otherwise)
break_frame- if true HSI will send/receive a break frame. Data buffers are ignored in the request.
-
struct
hsi_port¶ HSI port device
Definition
struct hsi_port {
struct device device;
struct hsi_config tx_cfg;
struct hsi_config rx_cfg;
unsigned int num;
unsigned int shared:1;
int claimed;
struct mutex lock;
int (*async)(struct hsi_msg *msg);
int (*setup)(struct hsi_client *cl);
int (*flush)(struct hsi_client *cl);
int (*start_tx)(struct hsi_client *cl);
int (*stop_tx)(struct hsi_client *cl);
int (*release)(struct hsi_client *cl);
struct blocking_notifier_head n_head;
};
Members
device- Driver model representation of the device
tx_cfg- Current TX path configuration
rx_cfg- Current RX path configuration
num- Port number
shared- Set when port can be shared by different clients
claimed- Reference count of clients which claimed the port
lock- Serialize port claim
async- Asynchronous transfer callback
setup- Callback to set the HSI client configuration
flush- Callback to clean the HW state and destroy all pending transfers
start_tx- Callback to inform that a client wants to TX data
stop_tx- Callback to inform that a client no longer wishes to TX data
release- Callback to inform that a client no longer uses the port
n_head- Notifier chain for signaling port events to the clients.
-
struct
hsi_controller¶ HSI controller device
Definition
struct hsi_controller {
struct device device;
struct module *owner;
unsigned int id;
unsigned int num_ports;
struct hsi_port **port;
};
Members
device- Driver model representation of the device
owner- Pointer to the module owning the controller
id- HSI controller ID
num_ports- Number of ports in the HSI controller
port- Array of HSI ports
-
unsigned int
hsi_id(struct hsi_client *cl)¶ Get HSI controller ID associated to a client
Parameters
struct hsi_client *cl- Pointer to a HSI client
Description
Return the controller id where the client is attached to
-
unsigned int
hsi_port_id(struct hsi_client *cl)¶ Gets the port number a client is attached to
Parameters
struct hsi_client *cl- Pointer to HSI client
Description
Return the port number associated to the client
-
int
hsi_setup(struct hsi_client *cl)¶ Configure the client’s port
Parameters
struct hsi_client *cl- Pointer to the HSI client
Description
When sharing ports, clients should either relay on a single client setup or have the same setup for all of them.
Return -errno on failure, 0 on success
-
int
hsi_flush(struct hsi_client *cl)¶ Flush all pending transactions on the client’s port
Parameters
struct hsi_client *cl- Pointer to the HSI client
Description
This function will destroy all pending hsi_msg in the port and reset the HW port so it is ready to receive and transmit from a clean state.
Return -errno on failure, 0 on success
-
int
hsi_async_read(struct hsi_client *cl, struct hsi_msg *msg)¶ Submit a read transfer
Parameters
struct hsi_client *cl- Pointer to the HSI client
struct hsi_msg *msg- HSI message descriptor of the transfer
Description
Return -errno on failure, 0 on success
-
int
hsi_async_write(struct hsi_client *cl, struct hsi_msg *msg)¶ Submit a write transfer
Parameters
struct hsi_client *cl- Pointer to the HSI client
struct hsi_msg *msg- HSI message descriptor of the transfer
Description
Return -errno on failure, 0 on success
-
int
hsi_start_tx(struct hsi_client *cl)¶ Signal the port that the client wants to start a TX
Parameters
struct hsi_client *cl- Pointer to the HSI client
Description
Return -errno on failure, 0 on success
-
int
hsi_stop_tx(struct hsi_client *cl)¶ Signal the port that the client no longer wants to transmit
Parameters
struct hsi_client *cl- Pointer to the HSI client
Description
Return -errno on failure, 0 on success
Parameters
struct hsi_port *port- The HSI port to unregister
-
void
hsi_unregister_controller(struct hsi_controller *hsi)¶ Unregister an HSI controller
Parameters
struct hsi_controller *hsi- The HSI controller to register
-
int
hsi_register_controller(struct hsi_controller *hsi)¶ Register an HSI controller and its ports
Parameters
struct hsi_controller *hsi- The HSI controller to register
Description
Returns -errno on failure, 0 on success.
-
int
hsi_register_client_driver(struct hsi_client_driver *drv)¶ Register an HSI client to the HSI bus
Parameters
struct hsi_client_driver *drv- HSI client driver to register
Description
Returns -errno on failure, 0 on success.
-
void
hsi_put_controller(struct hsi_controller *hsi)¶ Free an HSI controller
Parameters
struct hsi_controller *hsi- Pointer to the HSI controller to freed
Description
HSI controller drivers should only use this function if they need to free their allocated hsi_controller structures before a successful call to hsi_register_controller. Other use is not allowed.
-
struct hsi_controller *
hsi_alloc_controller(unsigned int n_ports, gfp_t flags)¶ Allocate an HSI controller and its ports
Parameters
unsigned int n_ports- Number of ports on the HSI controller
gfp_t flags- Kernel allocation flags
Description
Return NULL on failure or a pointer to an hsi_controller on success.
Parameters
struct hsi_msg *msg- Pointer to the HSI message
Description
Client is responsible to free the buffers pointed by the scatterlists.
Parameters
unsigned int nents- Number of memory entries
gfp_t flags- Kernel allocation flags
Description
nents can be 0. This mainly makes sense for read transfer. In that case, HSI drivers will call the complete callback when there is data to be read without consuming it.
Return NULL on failure or a pointer to an hsi_msg on success.
-
int
hsi_async(struct hsi_client *cl, struct hsi_msg *msg)¶ Submit an HSI transfer to the controller
Parameters
struct hsi_client *cl- HSI client sending the transfer
struct hsi_msg *msg- The HSI transfer passed to controller
Description
The HSI message must have the channel, ttype, complete and destructor fields set beforehand. If nents > 0 then the client has to initialize also the scatterlists to point to the buffers to write to or read from.
HSI controllers relay on pre-allocated buffers from their clients and they do not allocate buffers on their own.
Once the HSI message transfer finishes, the HSI controller calls the complete callback with the status and actual_len fields of the HSI message updated. The complete callback can be called before returning from hsi_async.
Returns -errno on failure or 0 on success
-
int
hsi_claim_port(struct hsi_client *cl, unsigned int share)¶ Claim the HSI client’s port
Parameters
struct hsi_client *cl- HSI client that wants to claim its port
unsigned int share- Flag to indicate if the client wants to share the port or not.
Description
Returns -errno on failure, 0 on success.
-
void
hsi_release_port(struct hsi_client *cl)¶ Release the HSI client’s port
Parameters
struct hsi_client *cl- HSI client which previously claimed its port
-
int
hsi_register_port_event(struct hsi_client *cl, void (*handler)(struct hsi_client *, unsigned long))¶ Register a client to receive port events
Parameters
struct hsi_client *cl- HSI client that wants to receive port events
void (*handler)(struct hsi_client *, unsigned long)- Event handler callback
Description
Clients should register a callback to be able to receive events from the ports. Registration should happen after claiming the port. The handler can be called in interrupt context.
Returns -errno on error, or 0 on success.
-
int
hsi_unregister_port_event(struct hsi_client *cl)¶ Stop receiving port events for a client
Parameters
struct hsi_client *cl- HSI client that wants to stop receiving port events
Description
Clients should call this function before releasing their associated port.
Returns -errno on error, or 0 on success.
Parameters
struct hsi_port *port- Port where the event occurred
unsigned long event- The event type
Description
Clients should not be concerned about wake line behavior. However, due to a race condition in HSI HW protocol, clients need to be notified about wake line changes, so they can implement a workaround for it.
Events: HSI_EVENT_START_RX - Incoming wake line high HSI_EVENT_STOP_RX - Incoming wake line down
Returns -errno on error, or 0 on success.
-
int
hsi_get_channel_id_by_name(struct hsi_client *cl, char *name)¶ acquire channel id by channel name
Parameters
struct hsi_client *cl- HSI client, which uses the channel
char *name- name the channel is known under
Description
Clients can call this function to get the hsi channel ids similar to requesting IRQs or GPIOs by name. This function assumes the same channel configuration is used for RX and TX.
Returns -errno on error or channel id on success.