| 1 | High Speed Synchronous Serial Interface (HSI)
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| 2 | =============================================
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| 3 |
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| 4 | Introduction
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| 5 | ---------------
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| 6 |
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| 7 | High Speed Synchronous Interface (HSI) is a full duplex, low latency protocol,
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| 8 | that is optimized for die-level interconnect between an Application Processor
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| 9 | and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and
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| 10 | implemented by multiple vendors since then.
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| 11 |
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| 12 | The HSI interface supports full duplex communication over multiple channels
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| 13 | (typically 8) and is capable of reaching speeds up to 200 Mbit/s.
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| 14 |
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| 15 | The serial protocol uses two signals, DATA and FLAG as combined data and clock
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| 16 | signals and an additional READY signal for flow control. An additional WAKE
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| 17 | signal can be used to wakeup the chips from standby modes. The signals are
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| 18 | commonly prefixed by AC for signals going from the application die to the
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| 19 | cellular die and CA for signals going the other way around.
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| 20 |
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| 21 | ::
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| 22 |
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| 23 | +------------+ +---------------+
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| 24 | | Cellular | | Application |
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| 25 | | Die | | Die |
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| 26 | | | - - - - - - CAWAKE - - - - - - >| |
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| 27 | | T|------------ CADATA ------------>|R |
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| 28 | | X|------------ CAFLAG ------------>|X |
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| 29 | | |<----------- ACREADY ------------| |
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| 30 | | | | |
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| 31 | | | | |
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| 32 | | |< - - - - - ACWAKE - - - - - - -| |
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| 33 | | R|<----------- ACDATA -------------|T |
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| 34 | | X|<----------- ACFLAG -------------|X |
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| 35 | | |------------ CAREADY ----------->| |
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| 36 | | | | |
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| 37 | | | | |
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| 38 | +------------+ +---------------+
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| 39 |
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| 40 | HSI Subsystem in Linux
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| 41 | -------------------------
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| 42 |
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| 43 | In the Linux kernel the hsi subsystem is supposed to be used for HSI devices.
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| 44 | The hsi subsystem contains drivers for hsi controllers including support for
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| 45 | multi-port controllers and provides a generic API for using the HSI ports.
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| 46 |
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| 47 | It also contains HSI client drivers, which make use of the generic API to
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| 48 | implement a protocol used on the HSI interface. These client drivers can
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| 49 | use an arbitrary number of channels.
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| 50 |
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| 51 | hsi-char Device
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| 52 | ------------------
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| 53 |
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| 54 | Each port automatically registers a generic client driver called hsi_char,
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| 55 | which provides a character device for userspace representing the HSI port.
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| 56 | It can be used to communicate via HSI from userspace. Userspace may
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| 57 | configure the hsi_char device using the following ioctl commands:
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| 58 |
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| 59 | HSC_RESET
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| 60 | flush the HSI port
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| 61 |
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| 62 | HSC_SET_PM
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| 63 | enable or disable the client.
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| 64 |
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| 65 | HSC_SEND_BREAK
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| 66 | send break
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| 67 |
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| 68 | HSC_SET_RX
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| 69 | set RX configuration
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| 70 |
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| 71 | HSC_GET_RX
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| 72 | get RX configuration
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| 73 |
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| 74 | HSC_SET_TX
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| 75 | set TX configuration
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| 76 |
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| 77 | HSC_GET_TX
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| 78 | get TX configuration
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| 79 |
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| 80 | The kernel HSI API
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| 81 | ------------------
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| 82 |
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| 83 | .. kernel-doc:: include/linux/hsi/hsi.h
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| 84 | :internal:
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| 85 |
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| 86 | .. kernel-doc:: drivers/hsi/hsi_core.c
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| 87 | :export:
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| 88 |
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