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-rw-r--r--Documentation/i2c/busses/i2c-viapro8
-rw-r--r--Documentation/i2c/dev-interface110
-rw-r--r--Documentation/i2c/smbus-protocol4
-rw-r--r--Documentation/i2c/writing-clients4
4 files changed, 95 insertions, 31 deletions
diff --git a/Documentation/i2c/busses/i2c-viapro b/Documentation/i2c/busses/i2c-viapro
index 1405fb69984..22efedf60c8 100644
--- a/Documentation/i2c/busses/i2c-viapro
+++ b/Documentation/i2c/busses/i2c-viapro
@@ -16,6 +16,9 @@ Supported adapters:
* VIA Technologies, Inc. CX700
Datasheet: available on request and under NDA from VIA
+ * VIA Technologies, Inc. VX800/VX820
+ Datasheet: available on http://linux.via.com.tw
+
Authors:
Kyösti Mälkki <kmalkki@cc.hut.fi>,
Mark D. Studebaker <mdsxyz123@yahoo.com>,
@@ -49,6 +52,7 @@ Your lspci -n listing must show one of these :
device 1106:3372 (VT8237S)
device 1106:3287 (VT8251)
device 1106:8324 (CX700)
+ device 1106:8353 (VX800/VX820)
If none of these show up, you should look in the BIOS for settings like
enable ACPI / SMBus or even USB.
@@ -57,5 +61,5 @@ Except for the oldest chips (VT82C596A/B, VT82C686A and most probably
VT8231), this driver supports I2C block transactions. Such transactions
are mainly useful to read from and write to EEPROMs.
-The CX700 additionally appears to support SMBus PEC, although this driver
-doesn't implement it yet.
+The CX700/VX800/VX820 additionally appears to support SMBus PEC, although
+this driver doesn't implement it yet.
diff --git a/Documentation/i2c/dev-interface b/Documentation/i2c/dev-interface
index 9dd79123ddd..3e742ba2553 100644
--- a/Documentation/i2c/dev-interface
+++ b/Documentation/i2c/dev-interface
@@ -4,6 +4,10 @@ the /dev interface. You need to load module i2c-dev for this.
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 formated list of all
+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, ...,
@@ -17,30 +21,34 @@ So let's say you want to access an i2c adapter from a C program. The
first thing to do is "#include <linux/i2c-dev.h>". Please note that
there are two files named "i2c-dev.h" out there, one is distributed
with the Linux kernel and is meant to be included from kernel
-driver code, the other one is distributed with lm_sensors and is
+driver code, the other one is distributed with i2c-tools and is
meant to be included from user-space programs. You obviously want
the second one here.
Now, you have to decide which adapter you want to access. You should
-inspect /sys/class/i2c-dev/ to decide this. Adapter numbers are assigned
-somewhat dynamically, so you can not even assume /dev/i2c-0 is the
-first adapter.
+inspect /sys/class/i2c-dev/ or run "i2cdetect -l" to decide this.
+Adapter numbers are assigned somewhat dynamically, so you can not
+assume much about them. They can even change from one boot to the next.
Next thing, open the device file, as follows:
+
int file;
int adapter_nr = 2; /* probably dynamically determined */
char filename[20];
- sprintf(filename,"/dev/i2c-%d",adapter_nr);
- if ((file = open(filename,O_RDWR)) < 0) {
+ snprintf(filename, 19, "/dev/i2c-%d", adapter_nr);
+ file = open(filename, O_RDWR);
+ if (file < 0) {
/* ERROR HANDLING; you can check errno to see what went wrong */
exit(1);
}
When you have opened the device, you must specify with what device
address you want to communicate:
+
int addr = 0x40; /* The I2C address */
- if (ioctl(file,I2C_SLAVE,addr) < 0) {
+
+ if (ioctl(file, I2C_SLAVE, addr) < 0) {
/* ERROR HANDLING; you can check errno to see what went wrong */
exit(1);
}
@@ -48,31 +56,41 @@ address you want to communicate:
Well, you are all set up now. You can now use SMBus commands or plain
I2C to communicate with your device. SMBus commands are preferred if
the device supports them. Both are illustrated below.
+
__u8 register = 0x10; /* Device register to access */
__s32 res;
char buf[10];
+
/* Using SMBus commands */
- res = i2c_smbus_read_word_data(file,register);
+ res = i2c_smbus_read_word_data(file, register);
if (res < 0) {
/* ERROR HANDLING: i2c transaction failed */
} else {
/* res contains the read word */
}
+
/* Using I2C Write, equivalent of
- i2c_smbus_write_word_data(file,register,0x6543) */
+ i2c_smbus_write_word_data(file, register, 0x6543) */
buf[0] = register;
buf[1] = 0x43;
buf[2] = 0x65;
- if ( write(file,buf,3) != 3) {
+ if (write(file, buf, 3) ! =3) {
/* ERROR HANDLING: i2c transaction failed */
}
+
/* Using I2C Read, equivalent of i2c_smbus_read_byte(file) */
- if (read(file,buf,1) != 1) {
+ if (read(file, buf, 1) != 1) {
/* ERROR HANDLING: i2c transaction failed */
} else {
/* buf[0] contains the read byte */
}
+Note that only a subset of the I2C and SMBus protocols can be achieved by
+the means of read() and write() calls. In particular, so-called combined
+transactions (mixing read and write messages in the same transaction)
+aren't supported. For this reason, this interface is almost never used by
+user-space programs.
+
IMPORTANT: because of the use of inline functions, you *have* to use
'-O' or some variation when you compile your program!
@@ -80,31 +98,29 @@ IMPORTANT: because of the use of inline functions, you *have* to use
Full interface description
==========================
-The following IOCTLs are defined and fully supported
-(see also i2c-dev.h):
+The following IOCTLs are defined:
-ioctl(file,I2C_SLAVE,long addr)
+ioctl(file, I2C_SLAVE, long addr)
Change slave address. The address is passed in the 7 lower bits of the
argument (except for 10 bit addresses, passed in the 10 lower bits in this
case).
-ioctl(file,I2C_TENBIT,long select)
+ioctl(file, I2C_TENBIT, long select)
Selects ten bit addresses if select not equals 0, selects normal 7 bit
addresses if select equals 0. Default 0. This request is only valid
if the adapter has I2C_FUNC_10BIT_ADDR.
-ioctl(file,I2C_PEC,long select)
+ioctl(file, I2C_PEC, long select)
Selects SMBus PEC (packet error checking) generation and verification
if select not equals 0, disables if select equals 0. Default 0.
Used only for SMBus transactions. This request only has an effect if the
the adapter has I2C_FUNC_SMBUS_PEC; it is still safe if not, it just
doesn't have any effect.
-ioctl(file,I2C_FUNCS,unsigned long *funcs)
+ioctl(file, I2C_FUNCS, unsigned long *funcs)
Gets the adapter functionality and puts it in *funcs.
-ioctl(file,I2C_RDWR,struct i2c_rdwr_ioctl_data *msgset)
-
+ioctl(file, I2C_RDWR, struct i2c_rdwr_ioctl_data *msgset)
Do combined read/write transaction without stop in between.
Only valid if the adapter has I2C_FUNC_I2C. The argument is
a pointer to a
@@ -120,10 +136,9 @@ ioctl(file,I2C_RDWR,struct i2c_rdwr_ioctl_data *msgset)
The slave address and whether to use ten bit address mode has to be
set in each message, overriding the values set with the above ioctl's.
-
-Other values are NOT supported at this moment, except for I2C_SMBUS,
-which you should never directly call; instead, use the access functions
-below.
+ioctl(file, I2C_SMBUS, struct i2c_smbus_ioctl_data *args)
+ Not meant to be called directly; instead, use the access functions
+ below.
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
@@ -148,7 +163,52 @@ what happened. The 'write' transactions return 0 on success; the
returns the number of values read. The block buffers need not be longer
than 32 bytes.
-The above functions are all macros, that resolve to calls to the
-i2c_smbus_access function, that on its turn calls a specific ioctl
+The above functions are all inline functions, that resolve to calls to
+the i2c_smbus_access function, that on its turn calls a specific ioctl
with the data in a specific format. Read the source code if you
want to know what happens behind the screens.
+
+
+Implementation details
+======================
+
+For the interested, here's the code flow which happens inside the kernel
+when you use the /dev interface to I2C:
+
+1* Your program opens /dev/i2c-N and calls ioctl() on it, as described in
+section "C example" above.
+
+2* These open() and ioctl() calls are handled by the i2c-dev kernel
+driver: see i2c-dev.c:i2cdev_open() and i2c-dev.c:i2cdev_ioctl(),
+respectively. You can think of i2c-dev as a generic I2C chip driver
+that can be programmed from user-space.
+
+3* Some ioctl() calls are for administrative tasks and are handled by
+i2c-dev directly. Examples include I2C_SLAVE (set the address of the
+device you want to access) and I2C_PEC (enable or disable SMBus error
+checking on future transactions.)
+
+4* Other ioctl() calls are converted to in-kernel function calls by
+i2c-dev. Examples include I2C_FUNCS, which queries the I2C adapter
+functionality using i2c.h:i2c_get_functionality(), and I2C_SMBUS, which
+performs an SMBus transaction using i2c-core.c:i2c_smbus_xfer().
+
+The i2c-dev driver is responsible for checking all the parameters that
+come from user-space for validity. After this point, there is no
+difference between these calls that came from user-space through i2c-dev
+and calls that would have been performed by kernel I2C chip drivers
+directly. This means that I2C bus drivers don't need to implement
+anything special to support access from user-space.
+
+5* These i2c-core.c/i2c.h functions are wrappers to the actual
+implementation of your I2C bus driver. Each adapter must declare
+callback functions implementing these standard calls.
+i2c.h:i2c_get_functionality() calls i2c_adapter.algo->functionality(),
+while i2c-core.c:i2c_smbus_xfer() calls either
+adapter.algo->smbus_xfer() if it is implemented, or if not,
+i2c-core.c:i2c_smbus_xfer_emulated() which in turn calls
+i2c_adapter.algo->master_xfer().
+
+After your I2C bus driver has processed these requests, execution runs
+up the call chain, with almost no processing done, except by i2c-dev to
+package the returned data, if any, in suitable format for the ioctl.
diff --git a/Documentation/i2c/smbus-protocol b/Documentation/i2c/smbus-protocol
index 24bfb65da17..9df47441f0e 100644
--- a/Documentation/i2c/smbus-protocol
+++ b/Documentation/i2c/smbus-protocol
@@ -109,8 +109,8 @@ specified through the Comm byte.
S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] P
-SMBus Process Call
-==================
+SMBus Process Call: i2c_smbus_process_call()
+=============================================
This command selects a device register (through the Comm byte), sends
16 bits of data to it, and reads 16 bits of data in return.
diff --git a/Documentation/i2c/writing-clients b/Documentation/i2c/writing-clients
index 6b61b3a2e90..d73ee117a8c 100644
--- a/Documentation/i2c/writing-clients
+++ b/Documentation/i2c/writing-clients
@@ -606,6 +606,8 @@ SMBus communication
extern s32 i2c_smbus_read_word_data(struct i2c_client * client, u8 command);
extern s32 i2c_smbus_write_word_data(struct i2c_client * client,
u8 command, u16 value);
+ extern s32 i2c_smbus_process_call(struct i2c_client *client,
+ u8 command, u16 value);
extern s32 i2c_smbus_read_block_data(struct i2c_client * client,
u8 command, u8 *values);
extern s32 i2c_smbus_write_block_data(struct i2c_client * client,
@@ -621,8 +623,6 @@ These ones were removed from i2c-core because they had no users, but could
be added back later if needed:
extern s32 i2c_smbus_write_quick(struct i2c_client * client, u8 value);
- extern s32 i2c_smbus_process_call(struct i2c_client * client,
- u8 command, u16 value);
extern s32 i2c_smbus_block_process_call(struct i2c_client *client,
u8 command, u8 length,
u8 *values)
generated by cgit v1.2.3 (git 2.25.1) at 2024-12-04 21:51:05 +0000