platform/x86: asus-wmi: fix screenpad brightness range

[ Upstream commit 8d95d1f ]

Fix screenpad brightness range being too limited without reason:
testing this patch on a Zenbook Duo showed the hardware minimum not being
too low, therefore allow the user to configure the entire range, and
expose to userspace the hardware brightness range and value.

Fixes: 2c97d3e ("platform/x86: asus-wmi: add support for ASUS screenpad")
Signed-off-by: Denis Benato <denis.benato@linux.dev>
Signed-off-by: Luke Jones <luke@ljones.dev>
Link: https://patch.msgid.link/20260302174431.349816-3-denis.benato@linux.dev
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: NeroReflex

drivers/platform/x86/asus-wmi.c

@@ -127,7 +127,6 @@ module_param(fnlock_default, bool, 0444);
 #define NVIDIA_TEMP_MIN		75
 #define NVIDIA_TEMP_MAX		87
 
-#define ASUS_SCREENPAD_BRIGHT_MIN 20
 #define ASUS_SCREENPAD_BRIGHT_MAX 255
 #define ASUS_SCREENPAD_BRIGHT_DEFAULT 60
 
@@ -4143,13 +4142,13 @@ static int read_screenpad_brightness(struct backlight_device *bd)
 		return err;
 	/* The device brightness can only be read if powered, so return stored */
 	if (err == BACKLIGHT_POWER_OFF)
-		return asus->driver->screenpad_brightness - ASUS_SCREENPAD_BRIGHT_MIN;
+		return bd->props.brightness;
 
 	err = asus_wmi_get_devstate(asus, ASUS_WMI_DEVID_SCREENPAD_LIGHT, &retval);
 	if (err < 0)
 		return err;
 
-	return (retval & ASUS_WMI_DSTS_BRIGHTNESS_MASK) - ASUS_SCREENPAD_BRIGHT_MIN;
+	return retval & ASUS_WMI_DSTS_BRIGHTNESS_MASK;
 }
 
 static int update_screenpad_bl_status(struct backlight_device *bd)
@@ -4189,22 +4188,19 @@ static int asus_screenpad_init(struct asus_wmi *asus)
 	int err, power;
 	int brightness = 0;
 
-	power = read_screenpad_backlight_power(asus);
+	power = asus_wmi_get_devstate_simple(asus, ASUS_WMI_DEVID_SCREENPAD_POWER);
 	if (power < 0)
 		return power;
 
-	if (power != BACKLIGHT_POWER_OFF) {
+	if (power) {
 		err = asus_wmi_get_devstate(asus, ASUS_WMI_DEVID_SCREENPAD_LIGHT, &brightness);
 		if (err < 0)
 			return err;
 	}
-	/* default to an acceptable min brightness on boot if too low */
-	if (brightness < ASUS_SCREENPAD_BRIGHT_MIN)
-		brightness = ASUS_SCREENPAD_BRIGHT_DEFAULT;
 
 	memset(&props, 0, sizeof(struct backlight_properties));
 	props.type = BACKLIGHT_RAW; /* ensure this bd is last to be picked */
-	props.max_brightness = ASUS_SCREENPAD_BRIGHT_MAX - ASUS_SCREENPAD_BRIGHT_MIN;
+	props.max_brightness = ASUS_SCREENPAD_BRIGHT_MAX;
 	bd = backlight_device_register("asus_screenpad",
 				       &asus->platform_device->dev, asus,
 				       &asus_screenpad_bl_ops, &props);
@@ -4215,7 +4211,7 @@ static int asus_screenpad_init(struct asus_wmi *asus)
 
 	asus->screenpad_backlight_device = bd;
 	asus->driver->screenpad_brightness = brightness;
-	bd->props.brightness = brightness - ASUS_SCREENPAD_BRIGHT_MIN;
+	bd->props.brightness = brightness;
 	bd->props.power = power;
 	backlight_update_status(bd);