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 <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Hans de Goede <[e-mail]>
Signed-off-by: Hans de Goede <[e-mail]>

drivers/platform/x86/thinkpad_acpi.c

···
 	.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),
···
 	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)
···
 
 	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 */