tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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 <sre@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
+190
-190
+88
Documentation/driver-api/hsi.rst
+88
Documentation/driver-api/hsi.rst
···
1
+
High Speed Synchronous Serial Interface (HSI)
2
+
=============================================
3
+
4
+
Introduction
5
+
---------------
6
+
7
+
High Speed Syncronous Interface (HSI) is a fullduplex, low latency protocol,
8
+
that is optimized for die-level interconnect between an Application Processor
9
+
and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and
10
+
implemented by multiple vendors since then.
11
+
12
+
The HSI interface supports full duplex communication over multiple channels
13
+
(typically 8) and is capable of reaching speeds up to 200 Mbit/s.
14
+
15
+
The serial protocol uses two signals, DATA and FLAG as combined data and clock
16
+
signals and an additional READY signal for flow control. An additional WAKE
17
+
signal can be used to wakeup the chips from standby modes. The signals are
18
+
commonly prefixed by AC for signals going from the application die to the
19
+
cellular die and CA for signals going the other way around.
20
+
21
+
::
22
+
23
+
+------------+ +---------------+
24
+
| Cellular | | Application |
25
+
| Die | | Die |
26
+
| | - - - - - - CAWAKE - - - - - - >| |
27
+
| T|------------ CADATA ------------>|R |
28
+
| X|------------ CAFLAG ------------>|X |
29
+
| |<----------- ACREADY ------------| |
30
+
| | | |
31
+
| | | |
32
+
| |< - - - - - ACWAKE - - - - - - -| |
33
+
| R|<----------- ACDATA -------------|T |
34
+
| X|<----------- ACFLAG -------------|X |
35
+
| |------------ CAREADY ----------->| |
36
+
| | | |
37
+
| | | |
38
+
+------------+ +---------------+
39
+
40
+
HSI Subsystem in Linux
41
+
-------------------------
42
+
43
+
In the Linux kernel the hsi subsystem is supposed to be used for HSI devices.
44
+
The hsi subsystem contains drivers for hsi controllers including support for
45
+
multi-port controllers and provides a generic API for using the HSI ports.
46
+
47
+
It also contains HSI client drivers, which make use of the generic API to
48
+
implement a protocol used on the HSI interface. These client drivers can
49
+
use an arbitrary number of channels.
50
+
51
+
hsi-char Device
52
+
------------------
53
+
54
+
Each port automatically registers a generic client driver called hsi_char,
55
+
which provides a charecter device for userspace representing the HSI port.
56
+
It can be used to communicate via HSI from userspace. Userspace may
57
+
configure the hsi_char device using the following ioctl commands:
58
+
59
+
HSC_RESET
60
+
flush the HSI port
61
+
62
+
HSC_SET_PM
63
+
enable or disable the client.
64
+
65
+
HSC_SEND_BREAK
66
+
send break
67
+
68
+
HSC_SET_RX
69
+
set RX configuration
70
+
71
+
HSC_GET_RX
72
+
get RX configuration
73
+
74
+
HSC_SET_TX
75
+
set TX configuration
76
+
77
+
HSC_GET_TX
78
+
get TX configuration
79
+
80
+
The kernel HSI API
81
+
------------------
82
+
83
+
.. kernel-doc:: include/linux/hsi/hsi.h
84
+
:internal:
85
+
86
+
.. kernel-doc:: drivers/hsi/hsi_core.c
87
+
:export:
88
+
+46
Documentation/driver-api/i2c.rst
+46
Documentation/driver-api/i2c.rst
···
1
+
I\ :sup:`2`\ C and SMBus Subsystem
2
+
==================================
3
+
4
+
I\ :sup:`2`\ C (or without fancy typography, "I2C") is an acronym for
5
+
the "Inter-IC" bus, a simple bus protocol which is widely used where low
6
+
data rate communications suffice. Since it's also a licensed trademark,
7
+
some vendors use another name (such as "Two-Wire Interface", TWI) for
8
+
the same bus. I2C only needs two signals (SCL for clock, SDA for data),
9
+
conserving board real estate and minimizing signal quality issues. Most
10
+
I2C devices use seven bit addresses, and bus speeds of up to 400 kHz;
11
+
there's a high speed extension (3.4 MHz) that's not yet found wide use.
12
+
I2C is a multi-master bus; open drain signaling is used to arbitrate
13
+
between masters, as well as to handshake and to synchronize clocks from
14
+
slower clients.
15
+
16
+
The Linux I2C programming interfaces support only the master side of bus
17
+
interactions, not the slave side. The programming interface is
18
+
structured around two kinds of driver, and two kinds of device. An I2C
19
+
"Adapter Driver" abstracts the controller hardware; it binds to a
20
+
physical device (perhaps a PCI device or platform_device) and exposes a
21
+
:c:type:`struct i2c_adapter <i2c_adapter>` representing each
22
+
I2C bus segment it manages. On each I2C bus segment will be I2C devices
23
+
represented by a :c:type:`struct i2c_client <i2c_client>`.
24
+
Those devices will be bound to a :c:type:`struct i2c_driver
25
+
<i2c_driver>`, which should follow the standard Linux driver
26
+
model. (At this writing, a legacy model is more widely used.) There are
27
+
functions to perform various I2C protocol operations; at this writing
28
+
all such functions are usable only from task context.
29
+
30
+
The System Management Bus (SMBus) is a sibling protocol. Most SMBus
31
+
systems are also I2C conformant. The electrical constraints are tighter
32
+
for SMBus, and it standardizes particular protocol messages and idioms.
33
+
Controllers that support I2C can also support most SMBus operations, but
34
+
SMBus controllers don't support all the protocol options that an I2C
35
+
controller will. There are functions to perform various SMBus protocol
36
+
operations, either using I2C primitives or by issuing SMBus commands to
37
+
i2c_adapter devices which don't support those I2C operations.
38
+
39
+
.. kernel-doc:: include/linux/i2c.h
40
+
:internal:
41
+
42
+
.. kernel-doc:: drivers/i2c/i2c-boardinfo.c
43
+
:functions: i2c_register_board_info
44
+
45
+
.. kernel-doc:: drivers/i2c/i2c-core.c
46
+
:export:
+3
-1
Documentation/driver-api/index.rst
+3
-1
Documentation/driver-api/index.rst
-189
Documentation/driver-api/serial-interfaces.rst
-189
Documentation/driver-api/serial-interfaces.rst
···
1
-
Serial Peripheral Interface (SPI)
2
-
=================================
3
-
4
-
SPI is the "Serial Peripheral Interface", widely used with embedded
5
-
systems because it is a simple and efficient interface: basically a
6
-
multiplexed shift register. Its three signal wires hold a clock (SCK,
7
-
often in the range of 1-20 MHz), a "Master Out, Slave In" (MOSI) data
8
-
line, and a "Master In, Slave Out" (MISO) data line. SPI is a full
9
-
duplex protocol; for each bit shifted out the MOSI line (one per clock)
10
-
another is shifted in on the MISO line. Those bits are assembled into
11
-
words of various sizes on the way to and from system memory. An
12
-
additional chipselect line is usually active-low (nCS); four signals are
13
-
normally used for each peripheral, plus sometimes an interrupt.
14
-
15
-
The SPI bus facilities listed here provide a generalized interface to
16
-
declare SPI busses and devices, manage them according to the standard
17
-
Linux driver model, and perform input/output operations. At this time,
18
-
only "master" side interfaces are supported, where Linux talks to SPI
19
-
peripherals and does not implement such a peripheral itself. (Interfaces
20
-
to support implementing SPI slaves would necessarily look different.)
21
-
22
-
The programming interface is structured around two kinds of driver, and
23
-
two kinds of device. A "Controller Driver" abstracts the controller
24
-
hardware, which may be as simple as a set of GPIO pins or as complex as
25
-
a pair of FIFOs connected to dual DMA engines on the other side of the
26
-
SPI shift register (maximizing throughput). Such drivers bridge between
27
-
whatever bus they sit on (often the platform bus) and SPI, and expose
28
-
the SPI side of their device as a :c:type:`struct spi_master
29
-
<spi_master>`. SPI devices are children of that master,
30
-
represented as a :c:type:`struct spi_device <spi_device>` and
31
-
manufactured from :c:type:`struct spi_board_info
32
-
<spi_board_info>` descriptors which are usually provided by
33
-
board-specific initialization code. A :c:type:`struct spi_driver
34
-
<spi_driver>` is called a "Protocol Driver", and is bound to a
35
-
spi_device using normal driver model calls.
36
-
37
-
The I/O model is a set of queued messages. Protocol drivers submit one
38
-
or more :c:type:`struct spi_message <spi_message>` objects,
39
-
which are processed and completed asynchronously. (There are synchronous
40
-
wrappers, however.) Messages are built from one or more
41
-
:c:type:`struct spi_transfer <spi_transfer>` objects, each of
42
-
which wraps a full duplex SPI transfer. A variety of protocol tweaking
43
-
options are needed, because different chips adopt very different
44
-
policies for how they use the bits transferred with SPI.
45
-
46
-
.. kernel-doc:: include/linux/spi/spi.h
47
-
:internal:
48
-
49
-
.. kernel-doc:: drivers/spi/spi.c
50
-
:functions: spi_register_board_info
51
-
52
-
.. kernel-doc:: drivers/spi/spi.c
53
-
:export:
54
-
55
-
I\ :sup:`2`\ C and SMBus Subsystem
56
-
==================================
57
-
58
-
I\ :sup:`2`\ C (or without fancy typography, "I2C") is an acronym for
59
-
the "Inter-IC" bus, a simple bus protocol which is widely used where low
60
-
data rate communications suffice. Since it's also a licensed trademark,
61
-
some vendors use another name (such as "Two-Wire Interface", TWI) for
62
-
the same bus. I2C only needs two signals (SCL for clock, SDA for data),
63
-
conserving board real estate and minimizing signal quality issues. Most
64
-
I2C devices use seven bit addresses, and bus speeds of up to 400 kHz;
65
-
there's a high speed extension (3.4 MHz) that's not yet found wide use.
66
-
I2C is a multi-master bus; open drain signaling is used to arbitrate
67
-
between masters, as well as to handshake and to synchronize clocks from
68
-
slower clients.
69
-
70
-
The Linux I2C programming interfaces support only the master side of bus
71
-
interactions, not the slave side. The programming interface is
72
-
structured around two kinds of driver, and two kinds of device. An I2C
73
-
"Adapter Driver" abstracts the controller hardware; it binds to a
74
-
physical device (perhaps a PCI device or platform_device) and exposes a
75
-
:c:type:`struct i2c_adapter <i2c_adapter>` representing each
76
-
I2C bus segment it manages. On each I2C bus segment will be I2C devices
77
-
represented by a :c:type:`struct i2c_client <i2c_client>`.
78
-
Those devices will be bound to a :c:type:`struct i2c_driver
79
-
<i2c_driver>`, which should follow the standard Linux driver
80
-
model. (At this writing, a legacy model is more widely used.) There are
81
-
functions to perform various I2C protocol operations; at this writing
82
-
all such functions are usable only from task context.
83
-
84
-
The System Management Bus (SMBus) is a sibling protocol. Most SMBus
85
-
systems are also I2C conformant. The electrical constraints are tighter
86
-
for SMBus, and it standardizes particular protocol messages and idioms.
87
-
Controllers that support I2C can also support most SMBus operations, but
88
-
SMBus controllers don't support all the protocol options that an I2C
89
-
controller will. There are functions to perform various SMBus protocol
90
-
operations, either using I2C primitives or by issuing SMBus commands to
91
-
i2c_adapter devices which don't support those I2C operations.
92
-
93
-
.. kernel-doc:: include/linux/i2c.h
94
-
:internal:
95
-
96
-
.. kernel-doc:: drivers/i2c/i2c-boardinfo.c
97
-
:functions: i2c_register_board_info
98
-
99
-
.. kernel-doc:: drivers/i2c/i2c-core.c
100
-
:export:
101
-
102
-
High Speed Synchronous Serial Interface (HSI)
103
-
=============================================
104
-
105
-
1. Introduction
106
-
---------------
107
-
108
-
High Speed Syncronous Interface (HSI) is a fullduplex, low latency protocol,
109
-
that is optimized for die-level interconnect between an Application Processor
110
-
and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and
111
-
implemented by multiple vendors since then.
112
-
113
-
The HSI interface supports full duplex communication over multiple channels
114
-
(typically 8) and is capable of reaching speeds up to 200 Mbit/s.
115
-
116
-
The serial protocol uses two signals, DATA and FLAG as combined data and clock
117
-
signals and an additional READY signal for flow control. An additional WAKE
118
-
signal can be used to wakeup the chips from standby modes. The signals are
119
-
commonly prefixed by AC for signals going from the application die to the
120
-
cellular die and CA for signals going the other way around.
121
-
122
-
::
123
-
124
-
+------------+ +---------------+
125
-
| Cellular | | Application |
126
-
| Die | | Die |
127
-
| | - - - - - - CAWAKE - - - - - - >| |
128
-
| T|------------ CADATA ------------>|R |
129
-
| X|------------ CAFLAG ------------>|X |
130
-
| |<----------- ACREADY ------------| |
131
-
| | | |
132
-
| | | |
133
-
| |< - - - - - ACWAKE - - - - - - -| |
134
-
| R|<----------- ACDATA -------------|T |
135
-
| X|<----------- ACFLAG -------------|X |
136
-
| |------------ CAREADY ----------->| |
137
-
| | | |
138
-
| | | |
139
-
+------------+ +---------------+
140
-
141
-
2. HSI Subsystem in Linux
142
-
-------------------------
143
-
144
-
In the Linux kernel the hsi subsystem is supposed to be used for HSI devices.
145
-
The hsi subsystem contains drivers for hsi controllers including support for
146
-
multi-port controllers and provides a generic API for using the HSI ports.
147
-
148
-
It also contains HSI client drivers, which make use of the generic API to
149
-
implement a protocol used on the HSI interface. These client drivers can
150
-
use an arbitrary number of channels.
151
-
152
-
3. hsi-char Device
153
-
------------------
154
-
155
-
Each port automatically registers a generic client driver called hsi_char,
156
-
which provides a charecter device for userspace representing the HSI port.
157
-
It can be used to communicate via HSI from userspace. Userspace may
158
-
configure the hsi_char device using the following ioctl commands:
159
-
160
-
HSC_RESET
161
-
flush the HSI port
162
-
163
-
HSC_SET_PM
164
-
enable or disable the client.
165
-
166
-
HSC_SEND_BREAK
167
-
send break
168
-
169
-
HSC_SET_RX
170
-
set RX configuration
171
-
172
-
HSC_GET_RX
173
-
get RX configuration
174
-
175
-
HSC_SET_TX
176
-
set TX configuration
177
-
178
-
HSC_GET_TX
179
-
get TX configuration
180
-
181
-
The kernel HSI API
182
-
------------------
183
-
184
-
.. kernel-doc:: include/linux/hsi/hsi.h
185
-
:internal:
186
-
187
-
.. kernel-doc:: drivers/hsi/hsi_core.c
188
-
:export:
189
-
+53
Documentation/driver-api/spi.rst
+53
Documentation/driver-api/spi.rst
···
1
+
Serial Peripheral Interface (SPI)
2
+
=================================
3
+
4
+
SPI is the "Serial Peripheral Interface", widely used with embedded
5
+
systems because it is a simple and efficient interface: basically a
6
+
multiplexed shift register. Its three signal wires hold a clock (SCK,
7
+
often in the range of 1-20 MHz), a "Master Out, Slave In" (MOSI) data
8
+
line, and a "Master In, Slave Out" (MISO) data line. SPI is a full
9
+
duplex protocol; for each bit shifted out the MOSI line (one per clock)
10
+
another is shifted in on the MISO line. Those bits are assembled into
11
+
words of various sizes on the way to and from system memory. An
12
+
additional chipselect line is usually active-low (nCS); four signals are
13
+
normally used for each peripheral, plus sometimes an interrupt.
14
+
15
+
The SPI bus facilities listed here provide a generalized interface to
16
+
declare SPI busses and devices, manage them according to the standard
17
+
Linux driver model, and perform input/output operations. At this time,
18
+
only "master" side interfaces are supported, where Linux talks to SPI
19
+
peripherals and does not implement such a peripheral itself. (Interfaces
20
+
to support implementing SPI slaves would necessarily look different.)
21
+
22
+
The programming interface is structured around two kinds of driver, and
23
+
two kinds of device. A "Controller Driver" abstracts the controller
24
+
hardware, which may be as simple as a set of GPIO pins or as complex as
25
+
a pair of FIFOs connected to dual DMA engines on the other side of the
26
+
SPI shift register (maximizing throughput). Such drivers bridge between
27
+
whatever bus they sit on (often the platform bus) and SPI, and expose
28
+
the SPI side of their device as a :c:type:`struct spi_master
29
+
<spi_master>`. SPI devices are children of that master,
30
+
represented as a :c:type:`struct spi_device <spi_device>` and
31
+
manufactured from :c:type:`struct spi_board_info
32
+
<spi_board_info>` descriptors which are usually provided by
33
+
board-specific initialization code. A :c:type:`struct spi_driver
34
+
<spi_driver>` is called a "Protocol Driver", and is bound to a
35
+
spi_device using normal driver model calls.
36
+
37
+
The I/O model is a set of queued messages. Protocol drivers submit one
38
+
or more :c:type:`struct spi_message <spi_message>` objects,
39
+
which are processed and completed asynchronously. (There are synchronous
40
+
wrappers, however.) Messages are built from one or more
41
+
:c:type:`struct spi_transfer <spi_transfer>` objects, each of
42
+
which wraps a full duplex SPI transfer. A variety of protocol tweaking
43
+
options are needed, because different chips adopt very different
44
+
policies for how they use the bits transferred with SPI.
45
+
46
+
.. kernel-doc:: include/linux/spi/spi.h
47
+
:internal:
48
+
49
+
.. kernel-doc:: drivers/spi/spi.c
50
+
:functions: spi_register_board_info
51
+
52
+
.. kernel-doc:: drivers/spi/spi.c
53
+
:export: