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- 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
- ------------------
- .. kernel-doc:: include/linux/hsi/hsi.h
- :internal:
- .. kernel-doc:: drivers/hsi/hsi_core.c
- :export:
|
