platform/x86: thinkpad_acpi: Fix reporting a non present second fan o…

…n some models

[ Upstream commit a10d509 ]

thinkpad_acpi was reporting 2 fans on a ThinkPad T14s gen 1, even though
the laptop has only 1 fan.

The second, not present fan always reads 65535 (-1 in 16 bit signed),
ignore fans which report 65535 to avoid reporting the non present fan.

Signed-off-by: Jelle van der Waa <jvanderwaa@redhat.com>
Link: https://lore.kernel.org/r/20221019194751.5392-1-jvanderwaa@redhat.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/platform/x86/thinkpad_acpi.c

@@ -263,6 +263,8 @@ enum tpacpi_hkey_event_t {
 #define TPACPI_DBG_BRGHT	0x0020
 #define TPACPI_DBG_MIXER	0x0040
 
+#define FAN_NOT_PRESENT		65535
+
 #define strlencmp(a, b) (strncmp((a), (b), strlen(b)))
 
 
@@ -8876,7 +8878,7 @@ static int __init fan_init(struct ibm_init_struct *iibm)
 			/* Try and probe the 2nd fan */
 			tp_features.second_fan = 1; /* needed for get_speed to work */
 			res = fan2_get_speed(&speed);
-			if (res >= 0) {
+			if (res >= 0 && speed != FAN_NOT_PRESENT) {
 				/* It responded - so let's assume it's there */
 				tp_features.second_fan = 1;
 				tp_features.second_fan_ctl = 1;