1 High Speed Synchronous Serial Interface (HSI) 2 ============================================= 3 4 Introduction 5 --------------- 6 7 High Speed Synchronous Interface (HSI) is a full duplex, low latency protocol, 8 that is optimized for die-level interconnect between an Application Processor 9 and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and 10 implemented by multiple vendors since then. 11 12 The HSI interface supports full duplex communication over multiple channels 13 (typically 8) and is capable of reaching speeds up to 200 Mbit/s. 14 15 The serial protocol uses two signals, DATA and FLAG as combined data and clock 16 signals and an additional READY signal for flow control. An additional WAKE 17 signal can be used to wakeup the chips from standby modes. The signals are 18 commonly prefixed by AC for signals going from the application die to the 19 cellular 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 40 HSI Subsystem in Linux 41 ------------------------- 42 43 In the Linux kernel the hsi subsystem is supposed to be used for HSI devices. 44 The hsi subsystem contains drivers for hsi controllers including support for 45 multi-port controllers and provides a generic API for using the HSI ports. 46 47 It also contains HSI client drivers, which make use of the generic API to 48 implement a protocol used on the HSI interface. These client drivers can 49 use an arbitrary number of channels. 50 51 hsi-char Device 52 ------------------ 53 54 Each port automatically registers a generic client driver called hsi_char, 55 which provides a character device for userspace representing the HSI port. 56 It can be used to communicate via HSI from userspace. Userspace may 57 configure the hsi_char device using the following ioctl commands: 58 59 HSC_RESET 60 flush the HSI port 61 62 HSC_SET_PM 63 enable or disable the client. 64 65 HSC_SEND_BREAK 66 send break 67 68 HSC_SET_RX 69 set RX configuration 70 71 HSC_GET_RX 72 get RX configuration 73 74 HSC_SET_TX 75 set TX configuration 76 77 HSC_GET_TX 78 get TX configuration 79 80 The kernel HSI API 81 ------------------ 82 83 .. kernel-doc:: include/linux/hsi/hsi.h 84 :internal: 85 86 .. kernel-doc:: drivers/hsi/hsi_core.c 87 :export: 88
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