platform/x86: thinkpad_acpi: Add quirk for ThinkPads without a fan

Some ThinkPad models, like the X1 Tablet 1st and 2nd Gen, are passively
cooled without any fan.  Currently, an entry in /proc/acpi/ibm/fan is
nevertheless created, and misleadingly shows
	status:		enabled
	speed:		65535
	level:		auto

This patch adds a TPACPI_FAN_NOFAN quirk definition and corresponding
handling to not initialize a fan interface at all.

For the time being, the quirk is only applied for X1 Tablet 2nd Gen
(types 20JB, 20JC; EC N1O...); further models (such as Gen1, types 20GG
and 20GH) can be added easily once tested.

Tested on a 20JCS00C00, BIOS N1OET58W (1.43), EC N1OHT34W.
Signed-off-by: Alexander Kobel <a-kobel@a-kobel.de>
Link: https://lore.kernel.org/r/12d4b825-a2b9-8cb7-6ed3-db4d66f46a60@a-kobel.deReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/thinkpad_acpi.c

@@ -8679,9 +8679,10 @@ static const struct attribute_group fan_driver_attr_group = {
 	.attrs = fan_driver_attributes,
 };
 
-#define TPACPI_FAN_Q1	0x0001		/* Unitialized HFSP */
-#define TPACPI_FAN_2FAN	0x0002		/* EC 0x31 bit 0 selects fan2 */
-#define TPACPI_FAN_2CTL	0x0004		/* selects fan2 control */
+#define TPACPI_FAN_Q1		0x0001		/* Uninitialized HFSP */
+#define TPACPI_FAN_2FAN		0x0002		/* EC 0x31 bit 0 selects fan2 */
+#define TPACPI_FAN_2CTL		0x0004		/* selects fan2 control */
+#define TPACPI_FAN_NOFAN	0x0008		/* no fan available */
 
 static const struct tpacpi_quirk fan_quirk_table[] __initconst = {
 	TPACPI_QEC_IBM('1', 'Y', TPACPI_FAN_Q1),
@@ -8702,6 +8703,7 @@ static const struct tpacpi_quirk fan_quirk_table[] __initconst = {
 	TPACPI_Q_LNV3('N', '4', '0', TPACPI_FAN_2CTL),	/* P1 / X1 Extreme (4nd gen) */
 	TPACPI_Q_LNV3('N', '3', '0', TPACPI_FAN_2CTL),	/* P15 (1st gen) / P15v (1st gen) */
 	TPACPI_Q_LNV3('N', '3', '2', TPACPI_FAN_2CTL),	/* X1 Carbon (9th gen) */
+	TPACPI_Q_LNV3('N', '1', 'O', TPACPI_FAN_NOFAN),	/* X1 Tablet (2nd gen) */
 };
 
 static int __init fan_init(struct ibm_init_struct *iibm)
@@ -8730,6 +8732,11 @@ static int __init fan_init(struct ibm_init_struct *iibm)
 	quirks = tpacpi_check_quirks(fan_quirk_table,
 				     ARRAY_SIZE(fan_quirk_table));
 
+	if (quirks & TPACPI_FAN_NOFAN) {
+		pr_info("No integrated ThinkPad fan available\n");
+		return -ENODEV;
+	}
+
 	if (gfan_handle) {
 		/* 570, 600e/x, 770e, 770x */
 		fan_status_access_mode = TPACPI_FAN_RD_ACPI_GFAN;