| Jonathan Corbet | 5e99578 | 2016-09-06 07:15:24 -0600 | [diff] [blame] | 1 | High Speed Synchronous Serial Interface (HSI) |
| 2 | ============================================= |
| 3 | |
| 4 | Introduction |
| 5 | --------------- |
| 6 | |
| 7 | High Speed Syncronous Interface (HSI) is a fullduplex, 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 charecter 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 | |