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docs: i2c: call it "I2C" consistently

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Uppercase "I2C" is used almost everywhere in the docs, but the lowercase
version "i2c" is used somewhere. Use the uppercase form consistently.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Acked-by: Peter Rosin <peda@axentia.se>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
This commit is contained in:
Luca Ceresoli 2020-01-29 16:19:29 +01:00 committed by Wolfram Sang
parent 020bc5b929
commit 2f07c05f14
8 changed files with 53 additions and 53 deletions
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18
Documentation/i2c/dev-interface.rst
View File

@ -2,26 +2,26 @@
I2C Device Interface
====================
Usually, i2c devices are controlled by a kernel driver. But it is also
Usually, I2C devices are controlled by a kernel driver. But it is also
possible to access all devices on an adapter from userspace, through
the /dev interface. You need to load module i2c-dev for this.
Each registered i2c adapter gets a number, counting from 0. You can
Each registered I2C adapter gets a number, counting from 0. You can
examine /sys/class/i2c-dev/ to see what number corresponds to which adapter.
Alternatively, you can run "i2cdetect -l" to obtain a formatted list of all
i2c adapters present on your system at a given time. i2cdetect is part of
I2C adapters present on your system at a given time. i2cdetect is part of
the i2c-tools package.
I2C device files are character device files with major device number 89
and a minor device number corresponding to the number assigned as
explained above. They should be called "i2c-%d" (i2c-0, i2c-1, ...,
i2c-10, ...). All 256 minor device numbers are reserved for i2c.
i2c-10, ...). All 256 minor device numbers are reserved for I2C.
C example
=========
So let's say you want to access an i2c adapter from a C program.
So let's say you want to access an I2C adapter from a C program.
First, you need to include these two headers::
#include <linux/i2c-dev.h>
@ -66,7 +66,7 @@ the device supports them. Both are illustrated below::
/* Using SMBus commands */
res = i2c_smbus_read_word_data(file, reg);
if (res < 0) {
/* ERROR HANDLING: i2c transaction failed */
/* ERROR HANDLING: I2C transaction failed */
} else {
/* res contains the read word */
}
@ -79,12 +79,12 @@ the device supports them. Both are illustrated below::
buf[1] = 0x43;
buf[2] = 0x65;
if (write(file, buf, 3) != 3) {
/* ERROR HANDLING: i2c transaction failed */
/* ERROR HANDLING: I2C transaction failed */
}
/* Using I2C Read, equivalent of i2c_smbus_read_byte(file) */
if (read(file, buf, 1) != 1) {
/* ERROR HANDLING: i2c transaction failed */
/* ERROR HANDLING: I2C transaction failed */
} else {
/* buf[0] contains the read byte */
}
@ -144,7 +144,7 @@ The following IOCTLs are defined:
If possible, use the provided ``i2c_smbus_*`` methods described below instead
of issuing direct ioctls.
You can do plain i2c transactions by using read(2) and write(2) calls.
You can do plain I2C transactions by using read(2) and write(2) calls.
You do not need to pass the address byte; instead, set it through
ioctl I2C_SLAVE before you try to access the device.

2
Documentation/i2c/dma-considerations.rst
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@ -2,7 +2,7 @@
Linux I2C and DMA
=================
Given that i2c is a low-speed bus, over which the majority of messages
Given that I2C is a low-speed bus, over which the majority of messages
transferred are small, it is not considered a prime user of DMA access. At this
time of writing, only 10% of I2C bus master drivers have DMA support
implemented. And the vast majority of transactions are so small that setting up

4
Documentation/i2c/i2c-protocol.rst
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@ -2,7 +2,7 @@
I2C Protocol
============
This document describes the i2c protocol. Or will, when it is finished :-)
This document describes the I2C protocol. Or will, when it is finished :-)
Key to symbols
==============
@ -57,7 +57,7 @@ Modified transactions
=====================
The following modifications to the I2C protocol can also be generated by
setting these flags for i2c messages. With the exception of I2C_M_NOSTART, they
setting these flags for I2C messages. With the exception of I2C_M_NOSTART, they
are usually only needed to work around device issues:
I2C_M_IGNORE_NAK:

66
Documentation/i2c/i2c-topology.rst
View File

@ -2,8 +2,8 @@
I2C topology
============
There are a couple of reasons for building more complex i2c topologies
than a straight-forward i2c bus with one adapter and one or more devices.
There are a couple of reasons for building more complex I2C topologies
than a straight-forward I2C bus with one adapter and one or more devices.
1. A mux may be needed on the bus to prevent address collisions.
@ -11,20 +11,20 @@ than a straight-forward i2c bus with one adapter and one or more devices.
may be needed to determine if it is ok to access the bus.
3. A device (particularly RF tuners) may want to avoid the digital noise
from the i2c bus, at least most of the time, and sits behind a gate
from the I2C bus, at least most of the time, and sits behind a gate
that has to be operated before the device can be accessed.
Etc
===
These constructs are represented as i2c adapter trees by Linux, where
These constructs are represented as I2C adapter trees by Linux, where
each adapter has a parent adapter (except the root adapter) and zero or
more child adapters. The root adapter is the actual adapter that issues
i2c transfers, and all adapters with a parent are part of an "i2c-mux"
I2C transfers, and all adapters with a parent are part of an "i2c-mux"
object (quoted, since it can also be an arbitrator or a gate).
Depending of the particular mux driver, something happens when there is
an i2c transfer on one of its child adapters. The mux driver can
an I2C transfer on one of its child adapters. The mux driver can
obviously operate a mux, but it can also do arbitration with an external
bus master or open a gate. The mux driver has two operations for this,
select and deselect. select is called before the transfer and (the
@ -34,7 +34,7 @@ optional) deselect is called after the transfer.
Locking
=======
There are two variants of locking available to i2c muxes, they can be
There are two variants of locking available to I2C muxes, they can be
mux-locked or parent-locked muxes. As is evident from below, it can be
useful to know if a mux is mux-locked or if it is parent-locked. The
following list was correct at the time of writing:
@ -45,7 +45,7 @@ In drivers/i2c/muxes/:
i2c-arb-gpio-challenge Parent-locked
i2c-mux-gpio Normally parent-locked, mux-locked iff
all involved gpio pins are controlled by the
same i2c root adapter that they mux.
same I2C root adapter that they mux.
i2c-mux-gpmux Normally parent-locked, mux-locked iff
specified in device-tree.
i2c-mux-ltc4306 Mux-locked
@ -54,7 +54,7 @@ i2c-mux-pca9541 Parent-locked
i2c-mux-pca954x Parent-locked
i2c-mux-pinctrl Normally parent-locked, mux-locked iff
all involved pinctrl devices are controlled
by the same i2c root adapter that they mux.
by the same I2C root adapter that they mux.
i2c-mux-reg Parent-locked
====================== =============================================
@ -83,9 +83,9 @@ Mux-locked muxes
Mux-locked muxes does not lock the entire parent adapter during the
full select-transfer-deselect transaction, only the muxes on the parent
adapter are locked. Mux-locked muxes are mostly interesting if the
select and/or deselect operations must use i2c transfers to complete
select and/or deselect operations must use I2C transfers to complete
their tasks. Since the parent adapter is not fully locked during the
full transaction, unrelated i2c transfers may interleave the different
full transaction, unrelated I2C transfers may interleave the different
stages of the transaction. This has the benefit that the mux driver
may be easier and cleaner to implement, but it has some caveats.
@ -109,14 +109,14 @@ ML2. It is not safe to build arbitrary topologies with two (or more)
ML3. A mux-locked mux cannot be used by a driver for auto-closing
gates/muxes, i.e. something that closes automatically after a given
number (one, in most cases) of i2c transfers. Unrelated i2c transfers
number (one, in most cases) of I2C transfers. Unrelated I2C transfers
may creep in and close prematurely.
ML4. If any non-i2c operation in the mux driver changes the i2c mux state,
ML4. If any non-I2C operation in the mux driver changes the I2C mux state,
the driver has to lock the root adapter during that operation.
Otherwise garbage may appear on the bus as seen from devices
behind the mux, when an unrelated i2c transfer is in flight during
the non-i2c mux-changing operation.
behind the mux, when an unrelated I2C transfer is in flight during
the non-I2C mux-changing operation.
==== =====================================================================
@ -137,14 +137,14 @@ Mux-locked Example
When there is an access to D1, this happens:
1. Someone issues an i2c-transfer to D1.
1. Someone issues an I2C-transfer to D1.
2. M1 locks muxes on its parent (the root adapter in this case).
3. M1 calls ->select to ready the mux.
4. M1 (presumably) does some i2c-transfers as part of its select.
These transfers are normal i2c-transfers that locks the parent
4. M1 (presumably) does some I2C-transfers as part of its select.
These transfers are normal I2C-transfers that locks the parent
adapter.
5. M1 feeds the i2c-transfer from step 1 to its parent adapter as a
normal i2c-transfer that locks the parent adapter.
5. M1 feeds the I2C-transfer from step 1 to its parent adapter as a
normal I2C-transfer that locks the parent adapter.
6. M1 calls ->deselect, if it has one.
7. Same rules as in step 4, but for ->deselect.
8. M1 unlocks muxes on its parent.
@ -159,8 +159,8 @@ Parent-locked muxes
Parent-locked muxes lock the parent adapter during the full select-
transfer-deselect transaction. The implication is that the mux driver
has to ensure that any and all i2c transfers through that parent
adapter during the transaction are unlocked i2c transfers (using e.g.
has to ensure that any and all I2C transfers through that parent
adapter during the transaction are unlocked I2C transfers (using e.g.
__i2c_transfer), or a deadlock will follow. There are a couple of
caveats.
@ -169,12 +169,12 @@ PL1. If you build a topology with a parent-locked mux being the child
of another mux, this might break a possible assumption from the
child mux that the root adapter is unused between its select op
and the actual transfer (e.g. if the child mux is auto-closing
and the parent mux issus i2c-transfers as part of its select).
and the parent mux issus I2C-transfers as part of its select).
This is especially the case if the parent mux is mux-locked, but
it may also happen if the parent mux is parent-locked.
PL2. If select/deselect calls out to other subsystems such as gpio,
pinctrl, regmap or iio, it is essential that any i2c transfers
pinctrl, regmap or iio, it is essential that any I2C transfers
caused by these subsystems are unlocked. This can be convoluted to
accomplish, maybe even impossible if an acceptably clean solution
is sought.
@ -197,15 +197,15 @@ Parent-locked Example
When there is an access to D1, this happens:
1. Someone issues an i2c-transfer to D1.
1. Someone issues an I2C-transfer to D1.
2. M1 locks muxes on its parent (the root adapter in this case).
3. M1 locks its parent adapter.
4. M1 calls ->select to ready the mux.
5. If M1 does any i2c-transfers (on this root adapter) as part of
its select, those transfers must be unlocked i2c-transfers so
5. If M1 does any I2C-transfers (on this root adapter) as part of
its select, those transfers must be unlocked I2C-transfers so
that they do not deadlock the root adapter.
6. M1 feeds the i2c-transfer from step 1 to the root adapter as an
unlocked i2c-transfer, so that it does not deadlock the parent
6. M1 feeds the I2C-transfer from step 1 to the root adapter as an
unlocked I2C-transfer, so that it does not deadlock the parent
adapter.
7. M1 calls ->deselect, if it has one.
8. Same rules as in step 5, but for ->deselect.
@ -240,7 +240,7 @@ and specifically when M2 requests its parent to lock, M1 passes
the buck to the root adapter).
This topology is bad if M2 is an auto-closing mux and M1->select
issues any unlocked i2c transfers on the root adapter that may leak
issues any unlocked I2C transfers on the root adapter that may leak
through and be seen by the M2 adapter, thus closing M2 prematurely.
@ -286,14 +286,14 @@ point.
This kind of topology is generally not suitable and should probably
be avoided. The reason is that M2 probably assumes that there will
be no i2c transfers during its calls to ->select and ->deselect, and
be no I2C transfers during its calls to ->select and ->deselect, and
if there are, any such transfers might appear on the slave side of M2
as partial i2c transfers, i.e. garbage or worse. This might cause
as partial I2C transfers, i.e. garbage or worse. This might cause
device lockups and/or other problems.
The topology is especially troublesome if M2 is an auto-closing
mux. In that case, any interleaved accesses to D4 might close M2
prematurely, as might any i2c-transfers part of M1->select.
prematurely, as might any I2C-transfers part of M1->select.
But if M2 is not making the above stated assumption, and if M2 is not
auto-closing, the topology is fine.

2
Documentation/i2c/instantiating-devices.rst
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@ -188,7 +188,7 @@ destroyed automatically when the driver which detected them is removed,
or when the underlying I2C bus is itself destroyed, whichever happens
first.
Those of you familiar with the i2c subsystem of 2.4 kernels and early 2.6
Those of you familiar with the I2C subsystem of 2.4 kernels and early 2.6
kernels will find out that this method 3 is essentially similar to what
was done there. Two significant differences are:

6
Documentation/i2c/old-module-parameters.rst
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@ -2,14 +2,14 @@
I2C device driver binding control from user-space
=================================================
Up to kernel 2.6.32, many i2c drivers used helper macros provided by
Up to kernel 2.6.32, many I2C drivers used helper macros provided by
<linux/i2c.h> which created standard module parameters to let the user
control how the driver would probe i2c buses and attach to devices. These
control how the driver would probe I2C buses and attach to devices. These
parameters were known as "probe" (to let the driver probe for an extra
address), "force" (to forcibly attach the driver to a given device) and
"ignore" (to prevent a driver from probing a given address).
With the conversion of the i2c subsystem to the standard device driver
With the conversion of the I2C subsystem to the standard device driver
binding model, it became clear that these per-module parameters were no
longer needed, and that a centralized implementation was possible. The new,
sysfs-based interface is described in the documentation file

4
Documentation/i2c/slave-interface.rst
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@ -59,7 +59,7 @@ The bus driver sends an event to the backend using the following function::
ret = i2c_slave_event(client, event, &val)
'client' describes the i2c slave device. 'event' is one of the special event
'client' describes the I2C slave device. 'event' is one of the special event
types described hereafter. 'val' holds an u8 value for the data byte to be
read/written and is thus bidirectional. The pointer to val must always be
provided even if val is not used for an event, i.e. don't use NULL here. 'ret'
@ -143,7 +143,7 @@ Bus driver support
If you want to add slave support to the bus driver:
* implement calls to register/unregister the slave and add those to the
struct i2c_algorithm. When registering, you probably need to set the i2c
struct i2c_algorithm. When registering, you probably need to set the I2C
slave address and enable slave specific interrupts. If you use runtime pm, you
should use pm_runtime_get_sync() because your device usually needs to be
powered on always to be able to detect its slave address. When unregistering,

4
Documentation/i2c/writing-clients.rst
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@ -95,7 +95,7 @@ to gather information from the client, or write new information to the
client.
I have found it useful to define foo_read and foo_write functions for this.
For some cases, it will be easier to call the i2c functions directly,
For some cases, it will be easier to call the I2C functions directly,
but many chips have some kind of register-value idea that can easily
be encapsulated.
@ -344,7 +344,7 @@ Plain I2C communication
int i2c_master_recv(struct i2c_client *client, char *buf, int count);
These routines read and write some bytes from/to a client. The client
contains the i2c address, so you do not have to include it. The second
contains the I2C address, so you do not have to include it. The second
parameter contains the bytes to read/write, the third the number of bytes
to read/write (must be less than the length of the buffer, also should be
less than 64k since msg.len is u16.) Returned is the actual number of bytes