drm/nouveau/drm/therm/fan: add a fallback if no fan control is specified in the vbios

This seems to be absolutely necessary for a lot of NV40.

Reported-by: gsgf on IRC/freenode
Signed-off-by: Martin Peres <martin.peres@free.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nvkm/subdev/therm/base.c

@@ -64,10 +64,9 @@ nvkm_therm_update_trip(struct nvkm_therm *therm)
 }
 
 static int
-nvkm_therm_update_linear(struct nvkm_therm *therm)
+nvkm_therm_compute_linear_duty(struct nvkm_therm *therm, u8 linear_min_temp,
+                               u8 linear_max_temp)
 {
-	u8  linear_min_temp = therm->fan->bios.linear_min_temp;
-	u8  linear_max_temp = therm->fan->bios.linear_max_temp;
 	u8  temp = therm->func->temp_get(therm);
 	u16 duty;
 
@@ -85,6 +84,21 @@ nvkm_therm_update_linear(struct nvkm_therm *therm)
 	return duty;
 }
 
+static int
+nvkm_therm_update_linear(struct nvkm_therm *therm)
+{
+	u8  min = therm->fan->bios.linear_min_temp;
+	u8  max = therm->fan->bios.linear_max_temp;
+	return nvkm_therm_compute_linear_duty(therm, min, max);
+}
+
+static int
+nvkm_therm_update_linear_fallback(struct nvkm_therm *therm)
+{
+	u8 max = therm->bios_sensor.thrs_fan_boost.temp;
+	return nvkm_therm_compute_linear_duty(therm, 30, max);
+}
+
 static void
 nvkm_therm_update(struct nvkm_therm *therm, int mode)
 {
@@ -119,6 +133,8 @@ nvkm_therm_update(struct nvkm_therm *therm, int mode)
 		case NVBIOS_THERM_FAN_OTHER:
 			if (therm->cstate)
 				duty = therm->cstate;
+			else
+				duty = nvkm_therm_update_linear_fallback(therm);
 			poll = false;
 			break;
 		}