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1High Speed Synchronous Serial Interface (HSI)2=============================================3 4Introduction5---------------6 7High Speed Synchronous Interface (HSI) is a full duplex, low latency protocol,8that is optimized for die-level interconnect between an Application Processor9and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and10implemented by multiple vendors since then.11 12The HSI interface supports full duplex communication over multiple channels13(typically 8) and is capable of reaching speeds up to 200 Mbit/s.14 15The serial protocol uses two signals, DATA and FLAG as combined data and clock16signals and an additional READY signal for flow control. An additional WAKE17signal can be used to wakeup the chips from standby modes. The signals are18commonly prefixed by AC for signals going from the application die to the19cellular die and CA for signals going the other way around.20 21::22 23 +------------+ +---------------+24 | Cellular | | Application |25 | Die | | Die |26 | | - - - - - - CAWAKE - - - - - - >| |27 | T|------------ CADATA ------------>|R |28 | X|------------ CAFLAG ------------>|X |29 | |<----------- ACREADY ------------| |30 | | | |31 | | | |32 | |< - - - - - ACWAKE - - - - - - -| |33 | R|<----------- ACDATA -------------|T |34 | X|<----------- ACFLAG -------------|X |35 | |------------ CAREADY ----------->| |36 | | | |37 | | | |38 +------------+ +---------------+39 40HSI Subsystem in Linux41-------------------------42 43In the Linux kernel the hsi subsystem is supposed to be used for HSI devices.44The hsi subsystem contains drivers for hsi controllers including support for45multi-port controllers and provides a generic API for using the HSI ports.46 47It also contains HSI client drivers, which make use of the generic API to48implement a protocol used on the HSI interface. These client drivers can49use an arbitrary number of channels.50 51hsi-char Device52------------------53 54Each port automatically registers a generic client driver called hsi_char,55which provides a character device for userspace representing the HSI port.56It can be used to communicate via HSI from userspace. Userspace may57configure the hsi_char device using the following ioctl commands:58 59HSC_RESET60 flush the HSI port61 62HSC_SET_PM63 enable or disable the client.64 65HSC_SEND_BREAK66 send break67 68HSC_SET_RX69 set RX configuration70 71HSC_GET_RX72 get RX configuration73 74HSC_SET_TX75 set TX configuration76 77HSC_GET_TX78 get TX configuration79 80The kernel HSI API81------------------82 83.. kernel-doc:: include/linux/hsi/hsi.h84 :internal:85 86.. kernel-doc:: drivers/hsi/hsi_core.c87 :export:88 89