4b2643d7d9
Let the drivers specify how many bytes they want to read with i2c_smbus_read_i2c_block_data(). So far, the block count was hard-coded to I2C_SMBUS_BLOCK_MAX (32), which did not make much sense. Many driver authors complained about this before, and I believe it's about time to fix it. Right now, authors have to do technically stupid things, such as individual byte reads or full-fledged I2C messaging, to work around the problem. We do not want to encourage that. I even found that some bus drivers (e.g. i2c-amd8111) already implemented I2C block read the "right" way, that is, they didn't follow the old, broken standard. The fact that it was never noticed before just shows how little i2c_smbus_read_i2c_block_data() was used, which isn't that surprising given how broken its prototype was so far. There are some obvious compatiblity considerations: * This changes the i2c_smbus_read_i2c_block_data() prototype. Users outside the kernel tree will notice at compilation time, and will have to update their code. * User-space has access to i2c_smbus_xfer() directly using i2c-dev, so the changed expectations would affect tools such as i2cdump. In order to preserve binary compatibility, we give I2C_SMBUS_I2C_BLOCK_DATA a new numeric value, and define I2C_SMBUS_I2C_BLOCK_BROKEN with the old numeric value. When i2c-dev receives a transaction with the old value, it can convert it to the new format on the fly. Signed-off-by: Jean Delvare <khali@linux-fr.org>
109 lines
3.0 KiB
Plaintext
109 lines
3.0 KiB
Plaintext
Kernel driver max6875
|
|
=====================
|
|
|
|
Supported chips:
|
|
* Maxim MAX6874, MAX6875
|
|
Prefix: 'max6875'
|
|
Addresses scanned: None (see below)
|
|
Datasheet:
|
|
http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf
|
|
|
|
Author: Ben Gardner <bgardner@wabtec.com>
|
|
|
|
|
|
Description
|
|
-----------
|
|
|
|
The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor.
|
|
It provides timed outputs that can be used as a watchdog, if properly wired.
|
|
It also provides 512 bytes of user EEPROM.
|
|
|
|
At reset, the MAX6875 reads the configuration EEPROM into its configuration
|
|
registers. The chip then begins to operate according to the values in the
|
|
registers.
|
|
|
|
The Maxim MAX6874 is a similar, mostly compatible device, with more intputs
|
|
and outputs:
|
|
vin gpi vout
|
|
MAX6874 6 4 8
|
|
MAX6875 4 3 5
|
|
|
|
See the datasheet for more information.
|
|
|
|
|
|
Sysfs entries
|
|
-------------
|
|
|
|
eeprom - 512 bytes of user-defined EEPROM space.
|
|
|
|
|
|
General Remarks
|
|
---------------
|
|
|
|
Valid addresses for the MAX6875 are 0x50 and 0x52.
|
|
Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56.
|
|
The driver does not probe any address, so you must force the address.
|
|
|
|
Example:
|
|
$ modprobe max6875 force=0,0x50
|
|
|
|
The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple
|
|
addresses. For example, for address 0x50, it also reserves 0x51.
|
|
The even-address instance is called 'max6875', the odd one is 'max6875 subclient'.
|
|
|
|
|
|
Programming the chip using i2c-dev
|
|
----------------------------------
|
|
|
|
Use the i2c-dev interface to access and program the chips.
|
|
Reads and writes are performed differently depending on the address range.
|
|
|
|
The configuration registers are at addresses 0x00 - 0x45.
|
|
Use i2c_smbus_write_byte_data() to write a register and
|
|
i2c_smbus_read_byte_data() to read a register.
|
|
The command is the register number.
|
|
|
|
Examples:
|
|
To write a 1 to register 0x45:
|
|
i2c_smbus_write_byte_data(fd, 0x45, 1);
|
|
|
|
To read register 0x45:
|
|
value = i2c_smbus_read_byte_data(fd, 0x45);
|
|
|
|
|
|
The configuration EEPROM is at addresses 0x8000 - 0x8045.
|
|
The user EEPROM is at addresses 0x8100 - 0x82ff.
|
|
|
|
Use i2c_smbus_write_word_data() to write a byte to EEPROM.
|
|
|
|
The command is the upper byte of the address: 0x80, 0x81, or 0x82.
|
|
The data word is the lower part of the address or'd with data << 8.
|
|
cmd = address >> 8;
|
|
val = (address & 0xff) | (data << 8);
|
|
|
|
Example:
|
|
To write 0x5a to address 0x8003:
|
|
i2c_smbus_write_word_data(fd, 0x80, 0x5a03);
|
|
|
|
|
|
Reading data from the EEPROM is a little more complicated.
|
|
Use i2c_smbus_write_byte_data() to set the read address and then
|
|
i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data.
|
|
|
|
Example:
|
|
To read data starting at offset 0x8100, first set the address:
|
|
i2c_smbus_write_byte_data(fd, 0x81, 0x00);
|
|
|
|
And then read the data
|
|
value = i2c_smbus_read_byte(fd);
|
|
|
|
or
|
|
|
|
count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer);
|
|
|
|
The block read should read 16 bytes.
|
|
0x84 is the block read command.
|
|
|
|
See the datasheet for more details.
|
|
|