hwmon: (pmbus) Add a PMBUS_NO_CAPABILITY platform data flag

Some PMBus chips don't respond with valid data when reading the
CAPABILITY register. Add a flag that device drivers can set so
that the PMBus core driver doesn't use CAPABILITY to determine it's
behavior.
Signed-off-by: Eddie James <eajames@linux.ibm.com>
Link: https://lore.kernel.org/r/20201222152640.27749-2-eajames@linux.ibm.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/pmbus/pmbus_core.c

@@ -2204,9 +2204,11 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data,
 	}
 
 	/* Enable PEC if the controller 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;
+	}
 
 	/*
 	 * Check if the chip is write protected. If it is, we can not clear

include/linux/pmbus.h

@@ -34,6 +34,15 @@
  */
 #define PMBUS_WRITE_PROTECTED	BIT(1)
 
+/*
+ * PMBUS_NO_CAPABILITY
+ *
+ * Some PMBus chips don't respond with valid data when reading the CAPABILITY
+ * register. For such chips, this flag should be set so that the PMBus core
+ * driver doesn't use CAPABILITY to determine it's behavior.
+ */
+#define PMBUS_NO_CAPABILITY			BIT(2)
+
 struct pmbus_platform_data {
 	u32 flags;		/* Device specific flags */