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Commit 70fc1f54 authored by Jonathan Corbet's avatar Jonathan Corbet
Browse files

docs: Pull the HSI documentation together 



The HSI subsystem documentation was split across hsi.txt and the
device-drivers docbook.  Now that the latter has been converted to Sphinx,
pull in the HSI document so that it's all in one place.

Acked-by: default avatarSebastian Reichel <sre@kernel.org>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent dcec3c8c

Documentation/driver-api/serial-interfaces.rst

+78 −4
Original line number Diff line number Diff line
@@ -102,10 +102,84 @@ i2c_adapter devices which don't support those I2C operations. 
High Speed Synchronous Serial Interface (HSI)

=============================================



High Speed Synchronous Serial Interface (HSI) is a serial interface

mainly used for connecting application engines (APE) with cellular modem

engines (CMT) in cellular handsets. HSI provides multiplexing for up to

16 logical channels, low-latency and full duplex communication.

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:

Documentation/hsi.txt

deleted100644 → 0
+0 −75
Original line number Diff line number Diff line 
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

MAINTAINERS

+1 −1
Original line number Diff line number Diff line
@@ -5606,7 +5606,7 @@ M: Sebastian Reichel <sre@kernel.org> 
T:	git git://git.kernel.org/pub/scm/linux/kernel/git/sre/linux-hsi.git

S:	Maintained

F:	Documentation/ABI/testing/sysfs-bus-hsi

F:	Documentation/hsi.txt

F:	Documentation/device-drivers/serial-interfaces.rst

F:	drivers/hsi/

F:	include/linux/hsi/

F:	include/uapi/linux/hsi/