mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-27 03:10:12 +00:00
![Sebastian Reichel](/assets/img/avatar_default.png)
Add a document, which gives a rough introduction about what HSI is and how its handled by the Linux kernel. Signed-off-by: Sebastian Reichel <sre@kernel.org> Reviewed-by: Pavel Machek <pavel@ucw.cz>
75 lines
2.9 KiB
Text
75 lines
2.9 KiB
Text
HSI - High-speed Synchronous Serial Interface
|
|
|
|
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
|