ACPI / fan: Fix error reading cur_state

On some platforms with ACPI4 variable speed fan, reading cur_state from
cooling device returns "invalid value" error. This confuses user space
applications.

This issue occurs as the current driver doesn't take account of
"FineGrainControl" from _FIF(Fan Information). When the "FineGrainControl"
is set, _FSL(FSL Set Level) takes argument as a percent, which doesn't
have to match from any control value from _FPS(Fan Performance States).
It is also possible that the Fan is not actually running at the requested
speed returning a lower speed.
On some platforms the BIOS is setting fan speed to a level during boot,
which will not have an exact match to _FPS control values. The current
implementation will treat this level as invalid value.

The simple change is to atleast return state corresponding to a maximum
control value in the _FPS compared to the current level.

Signed-off-by: Srinivas Pandruvada <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/acpi/fan.c

···
 
 	control = obj->package.elements[1].integer.value;
 	for (i = 0; i < fan->fps_count; i++) {
-		if (control == fan->fps[i].control)
+		/*
+		 * When Fine Grain Control is set, return the state
+		 * corresponding to maximum fan->fps[i].control
+		 * value compared to the current speed. Here the
+		 * fan->fps[] is sorted array with increasing speed.
+		 */
+		if (fan->fif.fine_grain_ctrl && control < fan->fps[i].control) {
+			i = (i > 0) ? i - 1 : 0;
 			break;
+		} else if (control == fan->fps[i].control) {
+			break;
+		}
 	}
 	if (i == fan->fps_count) {
 		dev_dbg(&device->dev, "Invalid control value returned\n");