hwmon: (pmbus/ltc2978) Add chip specific write_byte_data

Several of the manuals for devices supported by this driver describes
the need for a minimum wait time before the chip is ready to receive
next command.

This wait time is already implemented in the driver as a ltc_wait_ready
function with a driver defined wait time of 100 ms, and is considered
for specific devices before reading/writing data on the pmbus.

Since this driver uses the default pmbus_regulator_ops for the enable/
disable/is_enabled functions we should add a driver specific callback
for write_byte_data to prevent bypassing the wait time recommendations
for the following devices: ltc3880/ltc3882/ltc3883/ltc3884/ltc3886/
ltc3887/ltc3889/ltm4664/ltm4675/ltm4676/ltm4677/ltm4678/ltm4680/ltm4686/
ltm4700/ltc7880.

Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
Link: https://lore.kernel.org/r/20220428144039.2464667-4-marten.lindahl@axis.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/ltc2978.c

@@ -196,6 +196,17 @@ static int ltc_read_byte_data(struct i2c_client *client, int page, int reg)
 	return pmbus_read_byte_data(client, page, reg);
 }
 
+static int ltc_write_byte_data(struct i2c_client *client, int page, int reg, u8 value)
+{
+	int ret;
+
+	ret = ltc_wait_ready(client);
+	if (ret < 0)
+		return ret;
+
+	return pmbus_write_byte_data(client, page, reg, value);
+}
+
 static int ltc_write_byte(struct i2c_client *client, int page, u8 byte)
 {
 	int ret;
@@ -681,6 +692,7 @@ static int ltc2978_probe(struct i2c_client *client)
 	info = &data->info;
 	info->write_word_data = ltc2978_write_word_data;
 	info->write_byte = ltc_write_byte;
+	info->write_byte_data = ltc_write_byte_data;
 	info->read_word_data = ltc_read_word_data;
 	info->read_byte_data = ltc_read_byte_data;