89 lines
3.1 KiB
ReStructuredText
89 lines
3.1 KiB
ReStructuredText
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High Speed Synchronous Serial Interface (HSI)
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=============================================
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Introduction
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---------------
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High Speed Synchronous Interface (HSI) is a full duplex, low latency protocol,
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that is optimized for die-level interconnect between an Application Processor
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and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and
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implemented by multiple vendors since then.
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The HSI interface supports full duplex communication over multiple channels
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(typically 8) and is capable of reaching speeds up to 200 Mbit/s.
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The serial protocol uses two signals, DATA and FLAG as combined data and clock
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signals and an additional READY signal for flow control. An additional WAKE
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signal can be used to wakeup the chips from standby modes. The signals are
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commonly prefixed by AC for signals going from the application die to the
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cellular die and CA for signals going the other way around.
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::
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+------------+ +---------------+
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| Cellular | | Application |
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| Die | | Die |
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| | - - - - - - CAWAKE - - - - - - >| |
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| T|------------ CADATA ------------>|R |
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| X|------------ CAFLAG ------------>|X |
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| |<----------- ACREADY ------------| |
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| |< - - - - - ACWAKE - - - - - - -| |
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| R|<----------- ACDATA -------------|T |
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| X|<----------- ACFLAG -------------|X |
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| |------------ CAREADY ----------->| |
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+------------+ +---------------+
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HSI Subsystem in Linux
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-------------------------
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In the Linux kernel the hsi subsystem is supposed to be used for HSI devices.
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The hsi subsystem contains drivers for hsi controllers including support for
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multi-port controllers and provides a generic API for using the HSI ports.
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It also contains HSI client drivers, which make use of the generic API to
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implement a protocol used on the HSI interface. These client drivers can
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use an arbitrary number of channels.
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hsi-char Device
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------------------
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Each port automatically registers a generic client driver called hsi_char,
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which provides a character device for userspace representing the HSI port.
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It can be used to communicate via HSI from userspace. Userspace may
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configure the hsi_char device using the following ioctl commands:
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HSC_RESET
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flush the HSI port
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HSC_SET_PM
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enable or disable the client.
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HSC_SEND_BREAK
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send break
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HSC_SET_RX
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set RX configuration
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HSC_GET_RX
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get RX configuration
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HSC_SET_TX
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set TX configuration
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HSC_GET_TX
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get TX configuration
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The kernel HSI API
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------------------
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.. kernel-doc:: include/linux/hsi/hsi.h
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:internal:
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.. kernel-doc:: drivers/hsi/hsi_core.c
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:export:
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