hwmon: (pmbus_core) Check adapter PEC support

Currently, for Packet Error Checking (PEC) only the controller
is checked for support. This causes problems on the cisco-8000
platform where a SMBUS transaction errors are observed. This is
because PEC has to be enabled only if both controller and
adapter support it.

Added code to check PEC capability for adapter and enable it
only if both controller and adapter supports PEC.
Signed-off-by: Madhava Reddy Siddareddygari <msiddare@cisco.com>
[Upstream from SONiC https://github.com/Azure/sonic-linux-kernel/pull/215]
Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
Link: https://lore.kernel.org/r/20210605052700.541455-1-pmenzel@molgen.mpg.de
[groeck: Dropped unnecessary continuation line]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/pmbus_core.c

@@ -2216,11 +2216,14 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
 		data->has_status_word = true;
 	}
 
-	/* Enable PEC if the controller supports it */
+	/* Enable PEC if the controller and bus supports it */
 	if (!(data->flags & PMBUS_NO_CAPABILITY)) {
 		ret = i2c_smbus_read_byte_data(client, PMBUS_CAPABILITY);
-		if (ret >= 0 && (ret & PB_CAPABILITY_ERROR_CHECK))
-			client->flags |= I2C_CLIENT_PEC;
+		if (ret >= 0 && (ret & PB_CAPABILITY_ERROR_CHECK)) {
+			if (i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_PEC)) {
+				client->flags |= I2C_CLIENT_PEC;
+			}
+		}
 	}
 
 	/*