235b84fc86
Pull i2c updates from Wolfram Sang:
"This pull request contains:
- i2c core reorganization. One source file became too monolithic. It
is now split up, yet we still have the same named object as the
final output. This should ease maintenance.
- new drivers: ZTE ZX2967 family, ASPEED 24XX/25XX
- designware driver gained slave mode support
- xgene-slimpro driver gained ACPI support
- bigger overhaul for pca-platform driver
- the algo-bit module now supports messages with enforced STOP
- slightly bigger than usual set of driver updates and improvements
and with much appreciated quality assurance from Andy Shevchenko"
* 'i2c/for-4.13' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux: (51 commits)
i2c: Provide a stub for i2c_detect_slave_mode()
i2c: designware: Let slave adapter support be optional
i2c: designware: Make HW init functions static
i2c: designware: fix spelling mistakes
i2c: pca-platform: propagate error from i2c_pca_add_numbered_bus
i2c: pca-platform: correctly set algo_data.reset_chip
i2c: acpi: Do not create i2c-clients for LNXVIDEO ACPI devices
i2c: designware: enable SLAVE in platform module
i2c: designware: add SLAVE mode functions
i2c: zx2967: drop COMPILE_TEST dependency
i2c: zx2967: always use the same device when printing errors
i2c: pca-platform: use dev_warn/dev_info instead of printk
i2c: pca-platform: use device managed allocations
i2c: pca-platform: add devicetree awareness
i2c: pca-platform: switch to struct gpio_desc
dt-bindings: add bindings for i2c-pca-platform
i2c: cadance: fix ctrl/addr reg write order
i2c: zx2967: add i2c controller driver for ZTE's zx2967 family
dt: bindings: add documentation for zx2967 family i2c controller
i2c: algo-bit: add support for I2C_M_STOP
...
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48 lines
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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 the master side of bus
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interactions and 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 model. There
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are 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-base.c
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:export:
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.. kernel-doc:: drivers/i2c/i2c-core-smbus.c
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:export:
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