docs: split up serial-interfaces.rst
It never made sense to keep these documents together; move each into its own file. Drop the section numbering on hsi.txt on its way to its own file. Suggested-by: Sebastian Reichel <sre@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Jonathan Corbet
parent
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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 Syncronous Interface (HSI) is a fullduplex, 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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| | | |
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| | | |
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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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| | | |
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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 charecter 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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@ -0,0 +1,46 @@
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I\ :sup:`2`\ C and SMBus Subsystem
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==================================
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I\ :sup:`2`\ C (or without fancy typography, "I2C") is an acronym for
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the "Inter-IC" bus, a simple bus protocol which is widely used where low
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data rate communications suffice. Since it's also a licensed trademark,
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some vendors use another name (such as "Two-Wire Interface", TWI) for
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the same bus. I2C only needs two signals (SCL for clock, SDA for data),
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conserving board real estate and minimizing signal quality issues. Most
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I2C devices use seven bit addresses, and bus speeds of up to 400 kHz;
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there's a high speed extension (3.4 MHz) that's not yet found wide use.
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I2C is a multi-master bus; open drain signaling is used to arbitrate
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between masters, as well as to handshake and to synchronize clocks from
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slower clients.
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The Linux I2C programming interfaces support only the master side of bus
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interactions, not the slave side. The programming interface is
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structured around two kinds of driver, and two kinds of device. An I2C
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"Adapter Driver" abstracts the controller hardware; it binds to a
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physical device (perhaps a PCI device or platform_device) and exposes a
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:c:type:`struct i2c_adapter <i2c_adapter>` representing each
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I2C bus segment it manages. On each I2C bus segment will be I2C devices
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represented by a :c:type:`struct i2c_client <i2c_client>`.
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Those devices will be bound to a :c:type:`struct i2c_driver
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<i2c_driver>`, which should follow the standard Linux driver
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model. (At this writing, a legacy model is more widely used.) There are
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functions to perform various I2C protocol operations; at this writing
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all such functions are usable only from task context.
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The System Management Bus (SMBus) is a sibling protocol. Most SMBus
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systems are also I2C conformant. The electrical constraints are tighter
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for SMBus, and it standardizes particular protocol messages and idioms.
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Controllers that support I2C can also support most SMBus operations, but
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SMBus controllers don't support all the protocol options that an I2C
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controller will. There are functions to perform various SMBus protocol
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operations, either using I2C primitives or by issuing SMBus commands to
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i2c_adapter devices which don't support those I2C operations.
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.. kernel-doc:: include/linux/i2c.h
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:internal:
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.. kernel-doc:: drivers/i2c/i2c-boardinfo.c
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:functions: i2c_register_board_info
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.. kernel-doc:: drivers/i2c/i2c-core.c
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:export:
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@ -20,5 +20,7 @@ available subsections can be seen below.
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sound
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frame-buffer
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input
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serial-interfaces
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spi
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i2c
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hsi
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miscellaneous
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@ -1,189 +0,0 @@
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Serial Peripheral Interface (SPI)
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=================================
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SPI is the "Serial Peripheral Interface", widely used with embedded
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systems because it is a simple and efficient interface: basically a
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multiplexed shift register. Its three signal wires hold a clock (SCK,
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often in the range of 1-20 MHz), a "Master Out, Slave In" (MOSI) data
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line, and a "Master In, Slave Out" (MISO) data line. SPI is a full
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duplex protocol; for each bit shifted out the MOSI line (one per clock)
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another is shifted in on the MISO line. Those bits are assembled into
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words of various sizes on the way to and from system memory. An
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additional chipselect line is usually active-low (nCS); four signals are
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normally used for each peripheral, plus sometimes an interrupt.
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|
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The SPI bus facilities listed here provide a generalized interface to
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declare SPI busses and devices, manage them according to the standard
|
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Linux driver model, and perform input/output operations. At this time,
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only "master" side interfaces are supported, where Linux talks to SPI
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peripherals and does not implement such a peripheral itself. (Interfaces
|
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to support implementing SPI slaves would necessarily look different.)
|
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|
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The programming interface is structured around two kinds of driver, and
|
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two kinds of device. A "Controller Driver" abstracts the controller
|
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hardware, which may be as simple as a set of GPIO pins or as complex as
|
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a pair of FIFOs connected to dual DMA engines on the other side of the
|
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SPI shift register (maximizing throughput). Such drivers bridge between
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whatever bus they sit on (often the platform bus) and SPI, and expose
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the SPI side of their device as a :c:type:`struct spi_master
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<spi_master>`. SPI devices are children of that master,
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represented as a :c:type:`struct spi_device <spi_device>` and
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manufactured from :c:type:`struct spi_board_info
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<spi_board_info>` descriptors which are usually provided by
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board-specific initialization code. A :c:type:`struct spi_driver
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<spi_driver>` is called a "Protocol Driver", and is bound to a
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spi_device using normal driver model calls.
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The I/O model is a set of queued messages. Protocol drivers submit one
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or more :c:type:`struct spi_message <spi_message>` objects,
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which are processed and completed asynchronously. (There are synchronous
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wrappers, however.) Messages are built from one or more
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:c:type:`struct spi_transfer <spi_transfer>` objects, each of
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which wraps a full duplex SPI transfer. A variety of protocol tweaking
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options are needed, because different chips adopt very different
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policies for how they use the bits transferred with SPI.
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.. kernel-doc:: include/linux/spi/spi.h
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:internal:
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.. kernel-doc:: drivers/spi/spi.c
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:functions: spi_register_board_info
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.. kernel-doc:: drivers/spi/spi.c
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:export:
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I\ :sup:`2`\ C and SMBus Subsystem
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==================================
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I\ :sup:`2`\ C (or without fancy typography, "I2C") is an acronym for
|
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the "Inter-IC" bus, a simple bus protocol which is widely used where low
|
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data rate communications suffice. Since it's also a licensed trademark,
|
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some vendors use another name (such as "Two-Wire Interface", TWI) for
|
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the same bus. I2C only needs two signals (SCL for clock, SDA for data),
|
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conserving board real estate and minimizing signal quality issues. Most
|
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I2C devices use seven bit addresses, and bus speeds of up to 400 kHz;
|
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there's a high speed extension (3.4 MHz) that's not yet found wide use.
|
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I2C is a multi-master bus; open drain signaling is used to arbitrate
|
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between masters, as well as to handshake and to synchronize clocks from
|
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slower clients.
|
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|
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The Linux I2C programming interfaces support only the master side of bus
|
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interactions, not the slave side. The programming interface is
|
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structured around two kinds of driver, and two kinds of device. An I2C
|
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"Adapter Driver" abstracts the controller hardware; it binds to a
|
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physical device (perhaps a PCI device or platform_device) and exposes a
|
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:c:type:`struct i2c_adapter <i2c_adapter>` representing each
|
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I2C bus segment it manages. On each I2C bus segment will be I2C devices
|
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represented by a :c:type:`struct i2c_client <i2c_client>`.
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Those devices will be bound to a :c:type:`struct i2c_driver
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<i2c_driver>`, which should follow the standard Linux driver
|
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model. (At this writing, a legacy model is more widely used.) There are
|
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functions to perform various I2C protocol operations; at this writing
|
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all such functions are usable only from task context.
|
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|
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The System Management Bus (SMBus) is a sibling protocol. Most SMBus
|
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systems are also I2C conformant. The electrical constraints are tighter
|
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for SMBus, and it standardizes particular protocol messages and idioms.
|
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Controllers that support I2C can also support most SMBus operations, but
|
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SMBus controllers don't support all the protocol options that an I2C
|
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controller will. There are functions to perform various SMBus protocol
|
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operations, either using I2C primitives or by issuing SMBus commands to
|
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i2c_adapter devices which don't support those I2C operations.
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.. kernel-doc:: include/linux/i2c.h
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:internal:
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.. kernel-doc:: drivers/i2c/i2c-boardinfo.c
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:functions: i2c_register_board_info
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.. kernel-doc:: drivers/i2c/i2c-core.c
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:export:
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High Speed Synchronous Serial Interface (HSI)
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=============================================
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1. Introduction
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---------------
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High Speed Syncronous Interface (HSI) is a fullduplex, low latency protocol,
|
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that is optimized for die-level interconnect between an Application Processor
|
||||
and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and
|
||||
implemented by multiple vendors since then.
|
||||
|
||||
The HSI interface supports full duplex communication over multiple channels
|
||||
(typically 8) and is capable of reaching speeds up to 200 Mbit/s.
|
||||
|
||||
The serial protocol uses two signals, DATA and FLAG as combined data and clock
|
||||
signals and an additional READY signal for flow control. An additional WAKE
|
||||
signal can be used to wakeup the chips from standby modes. The signals are
|
||||
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 - - - - - - >| |
|
||||
| T|------------ CADATA ------------>|R |
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| X|------------ CAFLAG ------------>|X |
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| |<----------- ACREADY ------------| |
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| | | |
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| | | |
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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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| | | |
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+------------+ +---------------+
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2. HSI Subsystem in Linux
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-------------------------
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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
|
||||
multi-port controllers and provides a generic API for using the HSI ports.
|
||||
|
||||
It also contains HSI client drivers, which make use of the generic API to
|
||||
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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3. hsi-char Device
|
||||
------------------
|
||||
|
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Each port automatically registers a generic client driver called hsi_char,
|
||||
which provides a charecter device for userspace representing the HSI port.
|
||||
It can be used to communicate via HSI from userspace. Userspace may
|
||||
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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|
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HSC_SET_PM
|
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enable or disable the client.
|
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|
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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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|
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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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|
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@ -0,0 +1,53 @@
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Serial Peripheral Interface (SPI)
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=================================
|
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|
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SPI is the "Serial Peripheral Interface", widely used with embedded
|
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systems because it is a simple and efficient interface: basically a
|
||||
multiplexed shift register. Its three signal wires hold a clock (SCK,
|
||||
often in the range of 1-20 MHz), a "Master Out, Slave In" (MOSI) data
|
||||
line, and a "Master In, Slave Out" (MISO) data line. SPI is a full
|
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duplex protocol; for each bit shifted out the MOSI line (one per clock)
|
||||
another is shifted in on the MISO line. Those bits are assembled into
|
||||
words of various sizes on the way to and from system memory. An
|
||||
additional chipselect line is usually active-low (nCS); four signals are
|
||||
normally used for each peripheral, plus sometimes an interrupt.
|
||||
|
||||
The SPI bus facilities listed here provide a generalized interface to
|
||||
declare SPI busses and devices, manage them according to the standard
|
||||
Linux driver model, and perform input/output operations. At this time,
|
||||
only "master" side interfaces are supported, where Linux talks to SPI
|
||||
peripherals and does not implement such a peripheral itself. (Interfaces
|
||||
to support implementing SPI slaves would necessarily look different.)
|
||||
|
||||
The programming interface is structured around two kinds of driver, and
|
||||
two kinds of device. A "Controller Driver" abstracts the controller
|
||||
hardware, which may be as simple as a set of GPIO pins or as complex as
|
||||
a pair of FIFOs connected to dual DMA engines on the other side of the
|
||||
SPI shift register (maximizing throughput). Such drivers bridge between
|
||||
whatever bus they sit on (often the platform bus) and SPI, and expose
|
||||
the SPI side of their device as a :c:type:`struct spi_master
|
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<spi_master>`. SPI devices are children of that master,
|
||||
represented as a :c:type:`struct spi_device <spi_device>` and
|
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manufactured from :c:type:`struct spi_board_info
|
||||
<spi_board_info>` descriptors which are usually provided by
|
||||
board-specific initialization code. A :c:type:`struct spi_driver
|
||||
<spi_driver>` is called a "Protocol Driver", and is bound to a
|
||||
spi_device using normal driver model calls.
|
||||
|
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The I/O model is a set of queued messages. Protocol drivers submit one
|
||||
or more :c:type:`struct spi_message <spi_message>` objects,
|
||||
which are processed and completed asynchronously. (There are synchronous
|
||||
wrappers, however.) Messages are built from one or more
|
||||
:c:type:`struct spi_transfer <spi_transfer>` objects, each of
|
||||
which wraps a full duplex SPI transfer. A variety of protocol tweaking
|
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options are needed, because different chips adopt very different
|
||||
policies for how they use the bits transferred with SPI.
|
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|
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.. kernel-doc:: include/linux/spi/spi.h
|
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:internal:
|
||||
|
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.. kernel-doc:: drivers/spi/spi.c
|
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:functions: spi_register_board_info
|
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|
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.. kernel-doc:: drivers/spi/spi.c
|
||||
:export:
|
||||
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Reference in New Issue