hwmon: (nct6775) Only report VID if supported and enabled

VID is not always enabled (NCT6775, NCT6776) or supported (NCT6779).
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/nct6775.c

@@ -3401,6 +3401,8 @@ static int nct6775_probe(struct platform_device *pdev)
 	const u16 *reg_temp, *reg_temp_over, *reg_temp_hyst, *reg_temp_config;
 	const u16 *reg_temp_alternate, *reg_temp_crit;
 	int num_reg_temp;
+	bool have_vid = false;
+	u8 cr2a;
 
 	res = platform_get_resource(pdev, IORESOURCE_IO, 0);
 	if (!devm_request_region(&pdev->dev, res->start, IOREGION_LENGTH,
@@ -3769,17 +3771,31 @@ static int nct6775_probe(struct platform_device *pdev)
 	/* Initialize the chip */
 	nct6775_init_device(data);
 
-	data->vrm = vid_which_vrm();
 	err = superio_enter(sio_data->sioreg);
 	if (err)
 		return err;
 
+	cr2a = superio_inb(sio_data->sioreg, 0x2a);
+	switch (data->kind) {
+	case nct6775:
+		have_vid = (cr2a & 0x40);
+		break;
+	case nct6776:
+		have_vid = (cr2a & 0x60) == 0x40;
+		break;
+	case nct6779:
+		break;
+	}
+
 	/*
 	 * Read VID value
 	 * We can get the VID input values directly at logical device D 0xe3.
 	 */
-	superio_select(sio_data->sioreg, NCT6775_LD_VID);
-	data->vid = superio_inb(sio_data->sioreg, 0xe3);
+	if (have_vid) {
+		superio_select(sio_data->sioreg, NCT6775_LD_VID);
+		data->vid = superio_inb(sio_data->sioreg, 0xe3);
+		data->vrm = vid_which_vrm();
+	}
 
 	if (fan_debounce) {
 		u8 tmp;
@@ -3804,9 +3820,11 @@ static int nct6775_probe(struct platform_device *pdev)
 
 	superio_exit(sio_data->sioreg);
 
-	err = device_create_file(dev, &dev_attr_cpu0_vid);
-	if (err)
-		return err;
+	if (have_vid) {
+		err = device_create_file(dev, &dev_attr_cpu0_vid);
+		if (err)
+			return err;
+	}
 
 	err = nct6775_check_fan_inputs(sio_data, data);
 	if (err)