From 5e995786850e78b7950f6979a6bdd3990abc89cd Mon Sep 17 00:00:00 2001 From: Jonathan Corbet Date: Tue, 6 Sep 2016 07:15:24 -0600 Subject: [PATCH] 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 Signed-off-by: Jonathan Corbet --- Documentation/driver-api/hsi.rst | 88 ++++++++ Documentation/driver-api/i2c.rst | 46 +++++ Documentation/driver-api/index.rst | 4 +- .../driver-api/serial-interfaces.rst | 189 ------------------ Documentation/driver-api/spi.rst | 53 +++++ 5 files changed, 190 insertions(+), 190 deletions(-) create mode 100644 Documentation/driver-api/hsi.rst create mode 100644 Documentation/driver-api/i2c.rst delete mode 100644 Documentation/driver-api/serial-interfaces.rst create mode 100644 Documentation/driver-api/spi.rst diff --git a/Documentation/driver-api/hsi.rst b/Documentation/driver-api/hsi.rst new file mode 100644 index 000000000000..f9cec02b72a1 --- /dev/null +++ b/Documentation/driver-api/hsi.rst @@ -0,0 +1,88 @@ +High Speed Synchronous Serial Interface (HSI) +============================================= + +Introduction +--------------- + +High Speed Syncronous Interface (HSI) is a fullduplex, low latency protocol, +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 +cellular die and CA for signals going the other way around. + +:: + + +------------+ +---------------+ + | Cellular | | Application | + | Die | | Die | + | | - - - - - - CAWAKE - - - - - - >| | + | T|------------ CADATA ------------>|R | + | X|------------ CAFLAG ------------>|X | + | |<----------- ACREADY ------------| | + | | | | + | | | | + | |< - - - - - ACWAKE - - - - - - -| | + | R|<----------- ACDATA -------------|T | + | X|<----------- ACFLAG -------------|X | + | |------------ CAREADY ----------->| | + | | | | + | | | | + +------------+ +---------------+ + +HSI Subsystem in Linux +------------------------- + +In the Linux kernel the hsi subsystem is supposed to be used for HSI devices. +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 +use an arbitrary number of channels. + +hsi-char Device +------------------ + +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: + +HSC_RESET + flush the HSI port + +HSC_SET_PM + enable or disable the client. + +HSC_SEND_BREAK + send break + +HSC_SET_RX + set RX configuration + +HSC_GET_RX + get RX configuration + +HSC_SET_TX + set TX configuration + +HSC_GET_TX + get TX configuration + +The kernel HSI API +------------------ + +.. kernel-doc:: include/linux/hsi/hsi.h + :internal: + +.. kernel-doc:: drivers/hsi/hsi_core.c + :export: + diff --git a/Documentation/driver-api/i2c.rst b/Documentation/driver-api/i2c.rst new file mode 100644 index 000000000000..f3939f7852bd --- /dev/null +++ b/Documentation/driver-api/i2c.rst @@ -0,0 +1,46 @@ +I\ :sup:`2`\ C and SMBus Subsystem +================================== + +I\ :sup:`2`\ C (or without fancy typography, "I2C") is an acronym for +the "Inter-IC" bus, a simple bus protocol which is widely used where low +data rate communications suffice. Since it's also a licensed trademark, +some vendors use another name (such as "Two-Wire Interface", TWI) for +the same bus. I2C only needs two signals (SCL for clock, SDA for data), +conserving board real estate and minimizing signal quality issues. Most +I2C devices use seven bit addresses, and bus speeds of up to 400 kHz; +there's a high speed extension (3.4 MHz) that's not yet found wide use. +I2C is a multi-master bus; open drain signaling is used to arbitrate +between masters, as well as to handshake and to synchronize clocks from +slower clients. + +The Linux I2C programming interfaces support only the master side of bus +interactions, not the slave side. The programming interface is +structured around two kinds of driver, and two kinds of device. An I2C +"Adapter Driver" abstracts the controller hardware; it binds to a +physical device (perhaps a PCI device or platform_device) and exposes a +:c:type:`struct i2c_adapter ` representing each +I2C bus segment it manages. On each I2C bus segment will be I2C devices +represented by a :c:type:`struct i2c_client `. +Those devices will be bound to a :c:type:`struct i2c_driver +`, which should follow the standard Linux driver +model. (At this writing, a legacy model is more widely used.) There are +functions to perform various I2C protocol operations; at this writing +all such functions are usable only from task context. + +The System Management Bus (SMBus) is a sibling protocol. Most SMBus +systems are also I2C conformant. The electrical constraints are tighter +for SMBus, and it standardizes particular protocol messages and idioms. +Controllers that support I2C can also support most SMBus operations, but +SMBus controllers don't support all the protocol options that an I2C +controller will. There are functions to perform various SMBus protocol +operations, either using I2C primitives or by issuing SMBus commands to +i2c_adapter devices which don't support those I2C operations. + +.. kernel-doc:: include/linux/i2c.h + :internal: + +.. kernel-doc:: drivers/i2c/i2c-boardinfo.c + :functions: i2c_register_board_info + +.. kernel-doc:: drivers/i2c/i2c-core.c + :export: diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst index b50c41011e47..8e259c5d0322 100644 --- a/Documentation/driver-api/index.rst +++ b/Documentation/driver-api/index.rst @@ -20,5 +20,7 @@ available subsections can be seen below. sound frame-buffer input - serial-interfaces + spi + i2c + hsi miscellaneous diff --git a/Documentation/driver-api/serial-interfaces.rst b/Documentation/driver-api/serial-interfaces.rst deleted file mode 100644 index 07c58971a322..000000000000 --- a/Documentation/driver-api/serial-interfaces.rst +++ /dev/null @@ -1,189 +0,0 @@ -Serial Peripheral Interface (SPI) -================================= - -SPI is the "Serial Peripheral Interface", widely used with embedded -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 -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 -`. SPI devices are children of that master, -represented as a :c:type:`struct spi_device ` and -manufactured from :c:type:`struct spi_board_info -` descriptors which are usually provided by -board-specific initialization code. A :c:type:`struct spi_driver -` is called a "Protocol Driver", and is bound to a -spi_device using normal driver model calls. - -The I/O model is a set of queued messages. Protocol drivers submit one -or more :c:type:`struct 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 ` objects, each of -which wraps a full duplex SPI transfer. A variety of protocol tweaking -options are needed, because different chips adopt very different -policies for how they use the bits transferred with SPI. - -.. kernel-doc:: include/linux/spi/spi.h - :internal: - -.. kernel-doc:: drivers/spi/spi.c - :functions: spi_register_board_info - -.. kernel-doc:: drivers/spi/spi.c - :export: - -I\ :sup:`2`\ C and SMBus Subsystem -================================== - -I\ :sup:`2`\ C (or without fancy typography, "I2C") is an acronym for -the "Inter-IC" bus, a simple bus protocol which is widely used where low -data rate communications suffice. Since it's also a licensed trademark, -some vendors use another name (such as "Two-Wire Interface", TWI) for -the same bus. I2C only needs two signals (SCL for clock, SDA for data), -conserving board real estate and minimizing signal quality issues. Most -I2C devices use seven bit addresses, and bus speeds of up to 400 kHz; -there's a high speed extension (3.4 MHz) that's not yet found wide use. -I2C is a multi-master bus; open drain signaling is used to arbitrate -between masters, as well as to handshake and to synchronize clocks from -slower clients. - -The Linux I2C programming interfaces support only the master side of bus -interactions, not the slave side. The programming interface is -structured around two kinds of driver, and two kinds of device. An I2C -"Adapter Driver" abstracts the controller hardware; it binds to a -physical device (perhaps a PCI device or platform_device) and exposes a -:c:type:`struct i2c_adapter ` representing each -I2C bus segment it manages. On each I2C bus segment will be I2C devices -represented by a :c:type:`struct i2c_client `. -Those devices will be bound to a :c:type:`struct i2c_driver -`, which should follow the standard Linux driver -model. (At this writing, a legacy model is more widely used.) There are -functions to perform various I2C protocol operations; at this writing -all such functions are usable only from task context. - -The System Management Bus (SMBus) is a sibling protocol. Most SMBus -systems are also I2C conformant. The electrical constraints are tighter -for SMBus, and it standardizes particular protocol messages and idioms. -Controllers that support I2C can also support most SMBus operations, but -SMBus controllers don't support all the protocol options that an I2C -controller will. There are functions to perform various SMBus protocol -operations, either using I2C primitives or by issuing SMBus commands to -i2c_adapter devices which don't support those I2C operations. - -.. kernel-doc:: include/linux/i2c.h - :internal: - -.. kernel-doc:: drivers/i2c/i2c-boardinfo.c - :functions: i2c_register_board_info - -.. kernel-doc:: drivers/i2c/i2c-core.c - :export: - -High Speed Synchronous Serial Interface (HSI) -============================================= - -1. Introduction ---------------- - -High Speed Syncronous Interface (HSI) is a fullduplex, low latency protocol, -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 -cellular die and CA for signals going the other way around. - -:: - - +------------+ +---------------+ - | Cellular | | Application | - | Die | | Die | - | | - - - - - - CAWAKE - - - - - - >| | - | T|------------ CADATA ------------>|R | - | X|------------ CAFLAG ------------>|X | - | |<----------- ACREADY ------------| | - | | | | - | | | | - | |< - - - - - ACWAKE - - - - - - -| | - | R|<----------- ACDATA -------------|T | - | X|<----------- ACFLAG -------------|X | - | |------------ CAREADY ----------->| | - | | | | - | | | | - +------------+ +---------------+ - -2. HSI Subsystem in Linux -------------------------- - -In the Linux kernel the hsi subsystem is supposed to be used for HSI devices. -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 -use an arbitrary number of channels. - -3. hsi-char Device ------------------- - -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: - -HSC_RESET - flush the HSI port - -HSC_SET_PM - enable or disable the client. - -HSC_SEND_BREAK - send break - -HSC_SET_RX - set RX configuration - -HSC_GET_RX - get RX configuration - -HSC_SET_TX - set TX configuration - -HSC_GET_TX - get TX configuration - -The kernel HSI API ------------------- - -.. kernel-doc:: include/linux/hsi/hsi.h - :internal: - -.. kernel-doc:: drivers/hsi/hsi_core.c - :export: - diff --git a/Documentation/driver-api/spi.rst b/Documentation/driver-api/spi.rst new file mode 100644 index 000000000000..f64cb666498a --- /dev/null +++ b/Documentation/driver-api/spi.rst @@ -0,0 +1,53 @@ +Serial Peripheral Interface (SPI) +================================= + +SPI is the "Serial Peripheral Interface", widely used with embedded +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 +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 +`. SPI devices are children of that master, +represented as a :c:type:`struct spi_device ` and +manufactured from :c:type:`struct spi_board_info +` descriptors which are usually provided by +board-specific initialization code. A :c:type:`struct spi_driver +` is called a "Protocol Driver", and is bound to a +spi_device using normal driver model calls. + +The I/O model is a set of queued messages. Protocol drivers submit one +or more :c:type:`struct 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 ` objects, each of +which wraps a full duplex SPI transfer. A variety of protocol tweaking +options are needed, because different chips adopt very different +policies for how they use the bits transferred with SPI. + +.. kernel-doc:: include/linux/spi/spi.h + :internal: + +.. kernel-doc:: drivers/spi/spi.c + :functions: spi_register_board_info + +.. kernel-doc:: drivers/spi/spi.c + :export: