[PATCH] misc: i2c_eeprom: implement different probe test eeprom offset

[Heiko Schocher]

Hello Baruch,

Am 06.05.2020 um 18:47 schrieb Baruch Siach:
> Hi Eugen,
> 
> On Wed, May 06 2020, Eugen Hristev wrote:
>> Because of this commit :
>> 5ae84860b0 ("misc: i2c_eeprom: verify that the chip is functional at probe()")
>> at probe time, each eeprom is tested for read at offset 0.
>>
>> The Atmel AT24MAC402 eeprom has different mapping. One i2c slave address is
>> used for the lower 0x80 bytes and another i2c slave address is used for the
>> upper 0x80 bytes. Because of this basically the i2c master sees 2 different
>> slaves. We need the upper bytes because we read the unique MAC address from
>> this EEPROM area.
>>
>> However this implies that our slave address will return error on reads
>> from address 0x0 to 0x80.
>>
>> To solve this, implemented a way to figure out from the compatible udevice_id
>> 'data' field which offset we should attempt to read.
>> Added the offset as one byte in the data field (byte number 3).
>> Created two macros that will convert offset to 'data' field and back.
>>
>> The probe function will now read this offset and use it, instead of blindly
>> checking offset 0.
>>
>> This will fix the regression noticed on these EEPROMs since the commit
>> abovementioned that introduces the probe failed issue.
> 
> Judging from the Linux at24 driver that commit appears to break a number
> of other eeprom chips. I suggest to just revert it.

Hmm... how does the linux driver than work, as it has exact the same read?

See:
https://elixir.bootlin.com/linux/latest/source/drivers/misc/eeprom/at24.c#L710

So the fix from Eugen seems not too bad to me... but it should be
done also in linux ... or?

bye,
Heiko
> 
> baruch
> 
>>
>> The offset field can for sure be updated later at a 2byte offset if needed
>> by anyone.
>>
>> Signed-off-by: Eugen Hristev <eugen.hristev at microchip.com>
>> ---
>>   drivers/misc/i2c_eeprom.c | 18 ++++++++++++++++--
>>   1 file changed, 16 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/misc/i2c_eeprom.c b/drivers/misc/i2c_eeprom.c
>> index 3755dbf74b..79805cc46e 100644
>> --- a/drivers/misc/i2c_eeprom.c
>> +++ b/drivers/misc/i2c_eeprom.c
>> @@ -11,6 +11,13 @@
>>   #include <i2c.h>
>>   #include <i2c_eeprom.h>
>>   
>> +/* These macros are used to encode/decode the starting EEPROM offset into the
>> + * udevice_id structure's data field 3rd byte.
>> + * Lower 2 bytes of the data field are used for pagewidth.
>> + */
>> +#define I2C_EEPROM_OFFSET_TO_DATA(v) ((v) << 16)
>> +#define I2C_EEPROM_DATA_TO_OFFSET(v) ((v) >> 16)
>> +
>>   int i2c_eeprom_read(struct udevice *dev, int offset, uint8_t *buf, int size)
>>   {
>>   	const struct i2c_eeprom_ops *ops = device_get_ops(dev);
>> @@ -85,11 +92,17 @@ static int i2c_eeprom_std_ofdata_to_platdata(struct udevice *dev)
>>   
>>   static int i2c_eeprom_std_probe(struct udevice *dev)
>>   {
>> +	u64 data = dev_get_driver_data(dev);
>>   	u8 test_byte;
>>   	int ret;
>>   
>>   	/* Verify that the chip is functional */
>> -	ret = i2c_eeprom_read(dev, 0, &test_byte, 1);
>> +	/*
>> +	 * Not all eeproms start from offset 0. Valid offset is encoded in
>> +	 * upper bits of the data (byte 3).
>> +	 */
>> +	ret = i2c_eeprom_read(dev, I2C_EEPROM_DATA_TO_OFFSET(data) & 0xFF,
>> +			      &test_byte, 1);
>>   	if (ret)
>>   		return -ENODEV;
>>   
>> @@ -105,7 +118,8 @@ static const struct udevice_id i2c_eeprom_std_ids[] = {
>>   	{ .compatible = "atmel,24c08", .data = 4 },
>>   	{ .compatible = "atmel,24c08a", .data = 4 },
>>   	{ .compatible = "atmel,24c16a", .data = 4 },
>> -	{ .compatible = "atmel,24mac402", .data = 4 },
>> +	{ .compatible = "atmel,24mac402",
>> +		.data = (4 | I2C_EEPROM_OFFSET_TO_DATA(0x80))},
>>   	{ .compatible = "atmel,24c32", .data = 5 },
>>   	{ .compatible = "atmel,24c64", .data = 5 },
>>   	{ .compatible = "atmel,24c128", .data = 6 },
> 
> 

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