Documentation/driver-api/slimbus.rst

Source file repositories/reference/linux-study-clean/Documentation/driver-api/slimbus.rst

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Documentation/driver-api/slimbus.rst
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============================
Linux kernel SLIMbus support
============================

Overview
========

What is SLIMbus?
----------------
SLIMbus (Serial Low Power Interchip Media Bus) is a specification developed by
MIPI (Mobile Industry Processor Interface) alliance. The bus uses master/slave
configuration, and is a 2-wire multi-drop implementation (clock, and data).

Currently, SLIMbus is used to interface between application processors of SoCs
(System-on-Chip) and peripheral components (typically codec). SLIMbus uses
Time-Division-Multiplexing to accommodate multiple data channels, and
a control channel.

The control channel is used for various control functions such as bus
management, configuration and status updates. These messages can be unicast (e.g.
reading/writing device specific values), or multicast (e.g. data channel
reconfiguration sequence is a broadcast message announced to all devices)

A data channel is used for data-transfer between 2 SLIMbus devices. Data
channel uses dedicated ports on the device.

Hardware description:
---------------------
SLIMbus specification has different types of device classifications based on
their capabilities.
A manager device is responsible for enumeration, configuration, and dynamic
channel allocation. Every bus has 1 active manager.

A generic device is a device providing application functionality (e.g. codec).

Framer device is responsible for clocking the bus, and transmitting frame-sync
and framing information on the bus.

Each SLIMbus component has an interface device for monitoring physical layer.

Typically each SoC contains SLIMbus component having 1 manager, 1 framer device,
1 generic device (for data channel support), and 1 interface device.
External peripheral SLIMbus component usually has 1 generic device (for
functionality/data channel support), and an associated interface device.
The generic device's registers are mapped as 'value elements' so that they can
be written/read using SLIMbus control channel exchanging control/status type of
information.
In case there are multiple framer devices on the same bus, manager device is
responsible to select the active-framer for clocking the bus.

Per specification, SLIMbus uses "clock gears" to do power management based on
current frequency and bandwidth requirements. There are 10 clock gears and each
gear changes the SLIMbus frequency to be twice its previous gear.

Each device has a 6-byte enumeration-address and the manager assigns every
device with a 1-byte logical address after the devices report presence on the
bus.

Software description:
---------------------
There are 2 types of SLIMbus drivers:

slim_controller represents a 'controller' for SLIMbus. This driver should
implement duties needed by the SoC (manager device, associated
interface device for monitoring the layers and reporting errors, default
framer device).

slim_device represents the 'generic device/component' for SLIMbus, and a
slim_driver should implement driver for that slim_device.

Annotation

Implementation Notes