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

[Eugen Hristev]

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.

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 },
-- 
2.25.1