High Speed Synchronous Serial Interface (HSI)¶
Introduction¶
High Speed Synchronous Interface (HSI) is a full duplex, 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 character 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¶
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struct hsi_channel¶
channel resource used by the hsi clients
Definition:
struct hsi_channel {
unsigned int id;
const char *name;
};
Members
idChannel number
nameChannel name
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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
modeBit transmission mode (STREAM or FRAME)
channelsChannel resources used by the client
num_channelsNumber of channel resources
num_hw_channelsNumber of channels the transceiver is configured for [1..16]
speedMax bit transmission speed (Kbit/s)
{unnamed_union}anonymous
flowRX flow type (SYNCHRONIZED or PIPELINE)
arb_modeArbitration mode for TX frame (Round robin, priority)
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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
nameName for the HSI device
hsi_idHSI controller id where the client sits
portPort number in the controller where the client sits
tx_cfgHSI TX configuration
rx_cfgHSI RX configuration
platform_dataPlatform related data
archdataArchitecture-dependent device data
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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
deviceDriver model representation of the device
tx_cfgHSI TX configuration
rx_cfgHSI RX configuration
-
struct hsi_client_driver¶
Driver associated to an HSI client
Definition:
struct hsi_client_driver {
struct device_driver driver;
};
Members
driverDriver 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
linkFree to use by the current descriptor owner
clHSI device client that issues the transfer
sgtHead of the scatterlist array
contextClient context data associated to the transfer
completeTransfer completion callback
destructorDestructor to free resources when flushing
statusStatus of the transfer when completed
actual_lenActual length of data transferred on completion
channelChannel were to TX/RX the message
ttypeTransfer type (TX if set, RX otherwise)
break_frameif 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
deviceDriver model representation of the device
tx_cfgCurrent TX path configuration
rx_cfgCurrent RX path configuration
numPort number
sharedSet when port can be shared by different clients
claimedReference count of clients which claimed the port
lockSerialize port claim
asyncAsynchronous transfer callback
setupCallback to set the HSI client configuration
flushCallback to clean the HW state and destroy all pending transfers
start_txCallback to inform that a client wants to TX data
stop_txCallback to inform that a client no longer wishes to TX data
releaseCallback to inform that a client no longer uses the port
n_headNotifier 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
deviceDriver model representation of the device
ownerPointer to the module owning the controller
idHSI controller ID
num_portsNumber of ports in the HSI controller
portArray of HSI ports
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unsigned int hsi_id(struct hsi_client *cl)¶
Get HSI controller ID associated to a client
Parameters
struct hsi_client *clPointer to a HSI client
Description
Return the controller id where the client is attached to
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unsigned int hsi_port_id(struct hsi_client *cl)¶
Gets the port number a client is attached to
Parameters
struct hsi_client *clPointer to HSI client
Description
Return the port number associated to the client
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int hsi_setup(struct hsi_client *cl)¶
Configure the client’s port
Parameters
struct hsi_client *clPointer 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 *clPointer 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
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int hsi_async_read(struct hsi_client *cl, struct hsi_msg *msg)¶
Submit a read transfer
Parameters
struct hsi_client *clPointer to the HSI client
struct hsi_msg *msgHSI message descriptor of the transfer
Description
Return -errno on failure, 0 on success
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int hsi_async_write(struct hsi_client *cl, struct hsi_msg *msg)¶
Submit a write transfer
Parameters
struct hsi_client *clPointer to the HSI client
struct hsi_msg *msgHSI message descriptor of the transfer
Description
Return -errno on failure, 0 on success
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int hsi_start_tx(struct hsi_client *cl)¶
Signal the port that the client wants to start a TX
Parameters
struct hsi_client *clPointer to the HSI client
Description
Return -errno on failure, 0 on success
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int hsi_stop_tx(struct hsi_client *cl)¶
Signal the port that the client no longer wants to transmit
Parameters
struct hsi_client *clPointer to the HSI client
Description
Return -errno on failure, 0 on success
Parameters
struct hsi_port *portThe HSI port to unregister
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void hsi_unregister_controller(struct hsi_controller *hsi)¶
Unregister an HSI controller
Parameters
struct hsi_controller *hsiThe HSI controller to register
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int hsi_register_controller(struct hsi_controller *hsi)¶
Register an HSI controller and its ports
Parameters
struct hsi_controller *hsiThe HSI controller to register
Description
Returns -errno on failure, 0 on success.
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int hsi_register_client_driver(struct hsi_client_driver *drv)¶
Register an HSI client to the HSI bus
Parameters
struct hsi_client_driver *drvHSI client driver to register
Description
Returns -errno on failure, 0 on success.
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void hsi_put_controller(struct hsi_controller *hsi)¶
Free an HSI controller
Parameters
struct hsi_controller *hsiPointer 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.
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struct hsi_controller *hsi_alloc_controller(unsigned int n_ports, gfp_t flags)¶
Allocate an HSI controller and its ports
Parameters
unsigned int n_portsNumber of ports on the HSI controller
gfp_t flagsKernel allocation flags
Description
Return NULL on failure or a pointer to an hsi_controller on success.
Parameters
struct hsi_msg *msgPointer to the HSI message
Description
Client is responsible to free the buffers pointed by the scatterlists.
Parameters
unsigned int nentsNumber of memory entries
gfp_t flagsKernel 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.
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int hsi_async(struct hsi_client *cl, struct hsi_msg *msg)¶
Submit an HSI transfer to the controller
Parameters
struct hsi_client *clHSI client sending the transfer
struct hsi_msg *msgThe 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
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int hsi_claim_port(struct hsi_client *cl, unsigned int share)¶
Claim the HSI client’s port
Parameters
struct hsi_client *clHSI client that wants to claim its port
unsigned int shareFlag to indicate if the client wants to share the port or not.
Description
Returns -errno on failure, 0 on success.
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void hsi_release_port(struct hsi_client *cl)¶
Release the HSI client’s port
Parameters
struct hsi_client *clHSI client which previously claimed its port
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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 *clHSI 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.
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int hsi_unregister_port_event(struct hsi_client *cl)¶
Stop receiving port events for a client
Parameters
struct hsi_client *clHSI 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 *portPort where the event occurred
unsigned long eventThe 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.
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int hsi_get_channel_id_by_name(struct hsi_client *cl, char *name)¶
acquire channel id by channel name
Parameters
struct hsi_client *clHSI client, which uses the channel
char *namename 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.