i2c: rtl9300: do not set read mode on every transfer

Move the operation to set the read mode from config_xfer to probe.

The I2C controller of RTL9300 and RTL9310 support a legacy message mode
for READs with 'Read Address Data' instead of the standard format 'Write
Address ; Read Data'. There is no way to pass that via smbus_xfer, thus
there is no point in supported this in the driver and moreover no point
in setting this on every transaction. Setting this once in the probe
call is sufficient.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Tested-by: Sven Eckelmann <sven@narfation.org>
Reviewed-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Tested-by: Chris Packham <chris.packham@alliedtelesis.co.nz> # On RTL9302C based board
Tested-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20250927101931.71575-6-jelonek.jonas@gmail.com

Author: jonasjelonek

drivers/i2c/busses/i2c-rtl9300.c

@@ -130,11 +130,7 @@ static int rtl9300_i2c_config_xfer(struct rtl9300_i2c *i2c, struct rtl9300_i2c_c
 	if (ret)
 		return ret;
 
-	ret = regmap_field_write(i2c->fields[F_DATA_WIDTH], (len - 1) & 0xf);
-	if (ret)
-		return ret;
-
-	return regmap_field_write(i2c->fields[F_RD_MODE], 0);
+	return regmap_field_write(i2c->fields[F_DATA_WIDTH], (len - 1) & 0xf);
 }
 
 static int rtl9300_i2c_read(struct rtl9300_i2c *i2c, u8 *buf, int len)
@@ -455,6 +451,11 @@ static int rtl9300_i2c_probe(struct platform_device *pdev)
 	}
 	i2c->sda_num = 0xff;
 
+	/* only use standard read format */
+	ret = regmap_field_write(i2c->fields[F_RD_MODE], 0);
+	if (ret)
+		return ret;
+
 	return 0;
 }