Screenpad Plus Backlight Control

[Qonfused]

Backlight is set by ACPI calls exposed through a WMI driver. For reference, there is a linux module that probes ACPI for methods controlling backlight of the screenpad. Below details basic methods for the display's backlight control implemented similarly to keyboard backlight control in AsusSMC:

asus-wmi.h#L50-L74

50    | struct asus_wmi_driver {
51    | 	int			brightness;
52    | 	int			panel_power;
53    | 	int			wlan_ctrl_by_user;
54    | 
55    | 	const char		*name;
56    | 	struct module		*owner;
57    | 
58    | 	const char		*event_guid;
59    | 
60    | 	const struct key_entry	*keymap;
61    | 	const char		*input_name;
62    | 	const char		*input_phys;
63    | 	struct quirk_entry	*quirks;
64    | 	/* Returns new code, value, and autorelease values in arguments.
65    | 	 * Return ASUS_WMI_KEY_IGNORE in code if event should be ignored. */
66    | 	void (*key_filter) (struct asus_wmi_driver *driver, int *code,
67    | 			    unsigned int *value, bool *autorelease);
68    | 
69    | 	int (*probe) (struct platform_device *device);
70    | 	void (*detect_quirks) (struct asus_wmi_driver *driver);
71    | 
72    | 	struct platform_driver	platform_driver;
73    | 	struct platform_device *platform_device;
74    | };

asus-wmi.c#L819-L831

819   |	if (asus_wmi_dev_is_present(asus, ASUS_WMI_DEVID_SCREENPAD)
820   |		&& !screenpad_led_read(asus, &led_val)) {
821   |		asus->screenpad_led_wk = led_val;
822   |		INIT_WORK(&asus->screenpad_led_work, screenpad_led_update);
823   |
824   |		asus->screenpad_led.name = "asus::screenpad";
825   |		asus->screenpad_led.brightness_set = screenpad_led_set;
826   |		asus->screenpad_led.brightness_get = screenpad_led_get;
827   |		asus->screenpad_led.max_brightness = 0xff;
828   |
829   |		rv = led_classdev_register(&asus->platform_device->dev,
830   |					   &asus->screenpad_led);
831   |	}

If it can't be controlled in the same submenu as the primary display, then mapping Screenpad backlight brightness in a control center slider like keyboard brightness may be a good alternative UX implementation:

[Qonfused]

For reference, @shiecldk has a breakdown of EC events for the UX582 in hieplpvip/AsusSMC#102 (comment).

It's worth mentioning that SSDT-ASUSFN.aml in the original repo only has control logic for the primary display's backlight, and SSDT-AsusSMC.aml has logic for the ambient light sensor and keyboard backlight.

[Qonfused]

Continuing on the screenpad plus backlight discussion in #4 (comment)

In another thread, I also found mention of a WMNB method that controls backlight (refers to \_SB.ATKD.WMNB, which seems to be what wern-apfel was mentioning?): s-light/ASUS-ZenBook-Pro-Duo-UX581GV#1 (comment)

* Control backlight: `echo '\_SB.ATKD.WMNB 0x0 0x53564544 b32000500xx000000' | sudo tee /proc/acpi/call` (xx is a hex value from `00` to `FF`).

* Disable backlight: `echo '\_SB.ATKD.WMNB 0x0 0x53564544 b3100050000000000' | sudo tee /proc/acpi/call`

^^^ They're using the acpi_call linux kernel module to call this method, though assumedly an SSDT could also call the same method with these values to change backlight (and in your case disable backlight).

Below is the WMNB method that executes the above ACPI calls

// \_SB.ATKD.WMNB
54953 | Method (WMNB, 3, Serialized)
54954 | {
54955 |     CreateDWordField (Arg2, Zero, IIA0)
54956 |     CreateDWordField (Arg2, 0x04, IIA1)
54957 |     Local0 = (Arg1 & 0xFFFFFFFF)
...
55362 |     If ((Local0 == 0x53564544))
55363 |     {
...
55524 |         Name (TMBF, Buffer (0x02)
55525 |         {
55526 |             0x00, 0x00
55527 |         })
55528 |         If ((IIA0 == 0x00050031))
55529 |         {
55530 |             TMBF [Zero] = Zero
55531 |             Local0 = ^^PCI0.LPCB.EC0.REBC (0x12, 0x02)
55532 |             Local1 = DerefOf (Local0 [Zero])
55533 |             If ((IIA1 == One))
55534 |             {
55535 |                 Local1 &= 0xFD
55536 |             }
55537 |             Else
55538 |             {
55539 |                 Local1 |= 0x02
55540 |             }
55541 |         
55542 |             TMBF [One] = Local1
55543 |             Return (^^PCI0.LPCB.EC0.WEBC (0x13, 0x02, TMBF))
55544 |             Return (Zero)
55545 |         }
55546 |         
55547 |         If ((IIA0 == 0x00050032))
55548 |         {
55549 |             TMBF [One] = IIA1 /* \_SB_.ATKD.WMNB.IIA1 */
55550 |             TMBF [Zero] = One
55551 |             Return (^^PCI0.LPCB.EC0.WEBC (0x13, 0x02, TMBF))
55552 |             Return (Zero)
55553 |         }
55554 |         
55555 |         If ((IIA0 == 0x00050035))
55556 |         {
55557 |             TMBF [Zero] = Zero
55558 |             Local0 = ^^PCI0.LPCB.EC0.REBC (0x12, 0x02)
55559 |             Local1 = DerefOf (Local0 [Zero])
55560 |             If ((IIA1 == Zero))
55561 |             {
55562 |                 Local1 &= 0xF7
55563 |             }
55564 |             ElseIf ((IIA1 == One))
55565 |             {
55566 |                 Local1 |= 0x08
55567 |             }
55568 |         
55569 |             TMBF [One] = Local1
55570 |             Return (^^PCI0.LPCB.EC0.WEBC (0x13, 0x02, TMBF))
55571 |             Return (Zero)
55572 |         }

I have an example SSDT for disabling the screenpad plus display connector that writes to the EC's memory instead (based on @wern-apfel's SSDT-UX481FA.aml):

DISABLE-SCREENPAD.dsl
Disable the Screenpad Plus display connector

Rather than reading or writing to the embedded controller's memory directly (REBC/WEBC), the WMNB method (which handles all asus wmi functions) should be called instead:

External (\_SB.ATKD.WMNB, MethodObj)
// Sets the screenpad plus backlight intensity,
// where 'xx' is a hex value between 00 and FF.
\_SB.ATKD.WMNB(0x0, 0x53564544, /*b32000500xx000000*/)
// Disables screenpad plus until next backlight change.
\_SB.ATKD.WMNB(0x0, 0x53564544, /*b3100050000000000*/)

Some behavior can be ported to AsusSMC from the asus-wmi-screenpad repo.

[Qonfused]

Added refactor in 9de3d05.

[shiecldk]

Do you solve this with SSDT-SPLC.aml?

[Qonfused]

Yes. Its been fully implemented since the above PR, though an idea for #21 is to use an additional fake PNLF device to store and buffer backlight data to manipulate WMI methods. It should work more natively with those changes.