diff options
| -rw-r--r-- | drivers/i2c/mxc_i2c.c | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/drivers/i2c/mxc_i2c.c b/drivers/i2c/mxc_i2c.c index 5420afbc8e..f17a47f600 100644 --- a/drivers/i2c/mxc_i2c.c +++ b/drivers/i2c/mxc_i2c.c @@ -540,6 +540,25 @@ static int i2c_read_data(struct mxc_i2c_bus *i2c_bus, uchar chip, uchar *buf, #ifndef CONFIG_DM_I2C /* * Read data from I2C device + * + * The transactions use the syntax defined in the Linux kernel I2C docs. + * + * If alen is > 0, then this function will send a transaction of the form: + * S Chip Wr [A] Addr [A] S Chip Rd [A] [data] A ... NA P + * This is a normal I2C register read: writing the register address, then doing + * a repeated start and reading the data. + * + * If alen == 0, then we get this transaction: + * S Chip Wr [A] S Chip Rd [A] [data] A ... NA P + * This is somewhat unusual, though valid, transaction. It addresses the chip + * in write mode, but doesn't actually write any register address or data, then + * does a repeated start and reads data. + * + * If alen < 0, then we get this transaction: + * S Chip Rd [A] [data] A ... NA P + * The chip is addressed in read mode and then data is read. No register + * address is written first. This is perfectly valid on most devices and + * required on some (usually those that don't act like an array of registers). */ static int bus_i2c_read(struct mxc_i2c_bus *i2c_bus, u8 chip, u32 addr, int alen, u8 *buf, int len) @@ -574,6 +593,20 @@ static int bus_i2c_read(struct mxc_i2c_bus *i2c_bus, u8 chip, u32 addr, /* * Write data to I2C device + * + * If alen > 0, we get this transaction: + * S Chip Wr [A] addr [A] data [A] ... [A] P + * An ordinary write register command. + * + * If alen == 0, then we get this: + * S Chip Wr [A] data [A] ... [A] P + * This is a simple I2C write. + * + * If alen < 0, then we get this: + * S data [A] ... [A] P + * This is most likely NOT something that should be used. It doesn't send the + * chip address first, so in effect, the first byte of data will be used as the + * address. */ static int bus_i2c_write(struct mxc_i2c_bus *i2c_bus, u8 chip, u32 addr, int alen, const u8 *buf, int len) @@ -881,6 +914,7 @@ static int mxc_i2c_probe(struct udevice *bus) return 0; } +/* Sends: S Addr Wr [A|NA] P */ static int mxc_i2c_probe_chip(struct udevice *bus, u32 chip_addr, u32 chip_flags) { |