projects / mirror_ubuntu-bionic-kernel.git / blame
| Commit | Line | Data |
|---|---|---|
| 3a8ab8af SR |
1 | HSI - High-speed Synchronous Serial Interface |
| 2 | ||
| 3 | 1. Introduction | |
| 4 | ~~~~~~~~~~~~~~~ | |
| 5 | ||
| 6 | High Speed Syncronous Interface (HSI) is a fullduplex, low latency protocol, | |
| 7 | that is optimized for die-level interconnect between an Application Processor | |
| 8 | and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and | |
| 9 | implemented by multiple vendors since then. | |
| 10 | ||
| 11 | The HSI interface supports full duplex communication over multiple channels | |
| 12 | (typically 8) and is capable of reaching speeds up to 200 Mbit/s. | |
| 13 | ||
| 14 | The serial protocol uses two signals, DATA and FLAG as combined data and clock | |
| 15 | signals and an additional READY signal for flow control. An additional WAKE | |
| 16 | signal can be used to wakeup the chips from standby modes. The signals are | |
| 17 | commonly prefixed by AC for signals going from the application die to the | |
| 18 | cellular die and CA for signals going the other way around. | |
| 19 | ||
| 20 | +------------+ +---------------+ | |
| 21 | | Cellular | | Application | | |
| 22 | | Die | | Die | | |
| 23 | | | - - - - - - CAWAKE - - - - - - >| | | |
| 24 | | T|------------ CADATA ------------>|R | | |
| 25 | | X|------------ CAFLAG ------------>|X | | |
| 26 | | |<----------- ACREADY ------------| | | |
| 27 | | | | | | |
| 28 | | | | | | |
| 29 | | |< - - - - - ACWAKE - - - - - - -| | | |
| 30 | | R|<----------- ACDATA -------------|T | | |
| 31 | | X|<----------- ACFLAG -------------|X | | |
| 32 | | |------------ CAREADY ----------->| | | |
| 33 | | | | | | |
| 34 | | | | | | |
| 35 | +------------+ +---------------+ | |
| 36 | ||
| 37 | 2. HSI Subsystem in Linux | |
| 38 | ~~~~~~~~~~~~~~~~~~~~~~~~~ | |
| 39 | ||
| 40 | In the Linux kernel the hsi subsystem is supposed to be used for HSI devices. | |
| 41 | The hsi subsystem contains drivers for hsi controllers including support for | |
| 42 | multi-port controllers and provides a generic API for using the HSI ports. | |
| 43 | ||
| 44 | It also contains HSI client drivers, which make use of the generic API to | |
| 45 | implement a protocol used on the HSI interface. These client drivers can | |
| 46 | use an arbitrary number of channels. | |
| 47 | ||
| 48 | 3. hsi-char Device | |
| 49 | ~~~~~~~~~~~~~~~~~~ | |
| 50 | ||
| 51 | Each port automatically registers a generic client driver called hsi_char, | |
| 52 | which provides a charecter device for userspace representing the HSI port. | |
| 53 | It can be used to communicate via HSI from userspace. Userspace may | |
| 54 | configure the hsi_char device using the following ioctl commands: | |
| 55 | ||
| 56 | * HSC_RESET: | |
| 57 | - flush the HSI port | |
| 58 | ||
| 59 | * HSC_SET_PM | |
| 60 | - enable or disable the client. | |
| 61 | ||
| 62 | * HSC_SEND_BREAK | |
| 63 | - send break | |
| 64 | ||
| 65 | * HSC_SET_RX | |
| 66 | - set RX configuration | |
| 67 | ||
| 68 | * HSC_GET_RX | |
| 69 | - get RX configuration | |
| 70 | ||
| 71 | * HSC_SET_TX | |
| 72 | - set TX configuration | |
| 73 | ||
| 74 | * HSC_GET_TX | |
| 75 | - get TX configuration |