On 28/04/2022 13.11, Eugen Hristev wrote:
> According to at24c32 datasheet:
>
> RANDOM READ: A random read requires a “dummy” byte write sequence to load in
> the dataword address. Once the device address word and data word address are
> clocked in and acknowledged by the EEPROM, the microcontroller must generate
> another start condition.
>
> BYTE WRITE: A write operation requires two 8-bit data word addresses following
> the device address word and acknowledgment. Upon receipt of this address, the
> EEPROM will again respond with a zero and then clock in the first 8-bit data
> word.
>
> From this, my understanding is that dataword is 1 byte, and when reading the
> offset is just 1 byte.
Yes, you read data byte by byte, but that doesn't mean all those bytes
can be addressed using a single byte...
> drivers/misc/i2c_eeprom.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/misc/i2c_eeprom.c b/drivers/misc/i2c_eeprom.c
> index 89a450d0f8..c8c67cf028 100644
> --- a/drivers/misc/i2c_eeprom.c
> +++ b/drivers/misc/i2c_eeprom.c
> @@ -230,7 +230,7 @@ static const struct i2c_eeprom_drv_data atmel24c32_data =
> {
> .size = 4096,
> .pagesize = 32,
> .addr_offset_mask = 0,
> - .offset_len = 2,
> + .offset_len = 1,
> };
But this can't be correct, because how could one then possibly address
all 4096 bytes? Note that some eeproms larger than 256 bytes exist but
still use a 1-byte address; that's because they then respond to multiple
i2c addresses - that's what the "addr_offset_mask" is about.
Something else must be going on in your case, I think. Are you sure the
device tree is correct, i.e. that the eeprom is actually that one and
not one that does indeed use 1-byte addressing? I got curious and
downloaded the "SAM9X60-EK Board Design Files" from
https://www.microchip.com/en-us/development-tool/DT100126#Documentation,
inside which one finds mention of a "MCHP MEMORY SERIAL EEPROM 2Kb I2C
24AA025E48T-I/OT SOT-23-6", and 2Kb == 256 byte.
If you have the physical board handy, I'd try to locate the eeprom and
see what's printed on it.
Rasmus
