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

[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.

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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