[PATCH] Input: synaptics - support the touchpad LED on RMI function $30

[ahmad baghereslami <ahmad.b1995@gmail.com>]

Some HP laptops have an LED in the top left corner of the Synaptics
touchpad that HP's Windows driver lights while the touchpad is disabled
(double tap on that corner). On the HP ZBook 17 G3 (SYN3040, TM2706-002)
the LED is not driven through the PS/2 deluxe LED command: the Windows
driver (SynTP.sys 19.0.19.68) switches the touchpad to RMI register
access over PS/2 with mode byte 0x7f, looks up function $30 (GPIO/LED)
in the page description table and sets the LED bit in its control
register:

  register write:  SetScale 2:1, SetRate <reg>, SetRate <value>
  register read:   SetScale 2:1, SetRate <reg>, GetInfo (first byte)

For touchpads in a new rmi_led_pnp_ids list, look up the F30 LED this
way when the touchpad is set up and register a
synaptics::touchpad_disabled LED class device. Setting it deactivates
the touchpad, writes the F30 registers and restores the mode byte, which
leaves RMI access. The LED is restored after reconnect.

On this touchpad F30 is on page 1 with control base 0x55 and four
GPIO/LED pins; the LED is bit 3 of control register 0x59 and its
brightness register is 0x5f.

Tested on an HP ZBook 17 G3 with Ubuntu's 7.0.0 kernel: the LED follows
writes to its brightness file, the touchpad and the pointing stick keep
working, and a userspace helper that turns the touchpad off on a double
tap in the corner keeps the LED in step with GNOME's touchpad setting.

Reading HP's Windows driver (Ghidra) and writing this patch were done
with the help of an AI coding assistant (Claude); I tested the LED and
the touchpad on the machine.

Signed-off-by: ahmad baghereslami <ahmad.b1995@gmail.com>
---
 drivers/input/mouse/synaptics.c | 241 ++++++++++++++++++++++++++++++++
 drivers/input/mouse/synaptics.h |  13 ++
 2 files changed, 254 insertions(+)

diff --git a/drivers/input/mouse/synaptics.c b/drivers/input/mouse/synaptics.c
index b007e642e..bf1c6c738 100644
--- a/drivers/input/mouse/synaptics.c
+++ b/drivers/input/mouse/synaptics.c
@@ -589,6 +589,236 @@ static int synaptics_set_advanced_gesture_mode(struct psmouse *psmouse)
 	return 0;
 }
 
+/*
+ * Some HP touchpads have an LED in the top left corner that HP's Windows
+ * driver lights while the touchpad is disabled. It is wired to RMI function
+ * $30 (GPIO/LED), which these touchpads also expose over PS/2: mode byte 0x7f
+ * switches them to RMI register access, where SetScale 2:1 followed by two
+ * SetRate commands writes a register, and SetScale 2:1, SetRate and GetInfo
+ * read one. Setting the normal mode byte again leaves RMI access.
+ */
+static const char * const rmi_led_pnp_ids[] = {
+	"SYN3040", /* HP ZBook 17 G3 */
+	NULL
+};
+
+#define SYN_RMI_MODE			0x7f
+#define SYN_RMI_PAGE_SELECT		0xff
+#define SYN_RMI_PDT_START		0xee
+#define SYN_RMI_PDT_END			0x0b
+#define SYN_RMI_PDT_ENTRY_SIZE		6
+#define SYN_RMI_NUM_PAGES		4
+#define SYN_RMI_F30			0x30
+#define SYN_RMI_F30_HAS_LED		BIT(2)
+#define SYN_RMI_F30_HAS_GPIO		BIT(3)
+#define SYN_RMI_LED_BRIGHTNESS		0x0b	/* as set by HP's Windows driver */
+
+static int synaptics_rmi_write(struct psmouse *psmouse, u8 reg, u8 val)
+{
+	struct ps2dev *ps2dev = &psmouse->ps2dev;
+	int error;
+
+	error = ps2_command(ps2dev, NULL, PSMOUSE_CMD_SETSCALE21);
+	if (error)
+		return error;
+
+	error = ps2_command(ps2dev, &reg, PSMOUSE_CMD_SETRATE);
+	if (error)
+		return error;
+
+	return ps2_command(ps2dev, &val, PSMOUSE_CMD_SETRATE);
+}
+
+static int synaptics_rmi_read(struct psmouse *psmouse, u8 reg, u8 *val)
+{
+	struct ps2dev *ps2dev = &psmouse->ps2dev;
+	u8 param[3];
+	int error;
+
+	error = ps2_command(ps2dev, NULL, PSMOUSE_CMD_SETSCALE21);
+	if (error)
+		return error;
+
+	error = ps2_command(ps2dev, &reg, PSMOUSE_CMD_SETRATE);
+	if (error)
+		return error;
+
+	error = ps2_command(ps2dev, param, PSMOUSE_CMD_GETINFO);
+	if (error)
+		return error;
+
+	*val = param[0];
+	return 0;
+}
+
+/* Finds the LED of RMI function $30. Leaves the touchpad in RMI mode. */
+static int synaptics_rmi_led_probe(struct psmouse *psmouse)
+{
+	struct synaptics_data *priv = psmouse->private;
+	u8 fn, query, ctrl, caps, count, gpios;
+	unsigned int page, zeros, i;
+	int addr, error;
+
+	error = synaptics_mode_cmd(psmouse, SYN_RMI_MODE);
+	if (error)
+		return error;
+
+	for (page = 0; page < SYN_RMI_NUM_PAGES; page++) {
+		error = synaptics_rmi_write(psmouse, SYN_RMI_PAGE_SELECT, page);
+		if (error)
+			return error;
+
+		for (addr = SYN_RMI_PDT_START; addr >= SYN_RMI_PDT_END;
+		     addr -= SYN_RMI_PDT_ENTRY_SIZE) {
+			error = synaptics_rmi_read(psmouse, addr, &fn);
+			if (error)
+				return error;
+			if (!fn)
+				break;
+			if (fn != SYN_RMI_F30)
+				continue;
+
+			error = synaptics_rmi_read(psmouse, addr - 5, &query);
+			if (!error)
+				error = synaptics_rmi_read(psmouse, addr - 3, &ctrl);
+			if (!error)
+				error = synaptics_rmi_read(psmouse, query, &caps);
+			if (!error)
+				error = synaptics_rmi_read(psmouse, query + 1, &count);
+			if (error)
+				return error;
+
+			if (!(caps & SYN_RMI_F30_HAS_LED))
+				return -ENODEV;
+
+			priv->rmi_led_page = page;
+			if (!(caps & SYN_RMI_F30_HAS_GPIO)) {
+				priv->rmi_led_mask = BIT(0);
+				priv->rmi_led_ctrl = ctrl + 1;
+				priv->rmi_led_brightness = ctrl + 4;
+				return 0;
+			}
+
+			/* GPIO/LED select: the LED is the first set bit */
+			error = synaptics_rmi_read(psmouse, ctrl, &gpios);
+			if (error)
+				return error;
+
+			priv->rmi_led_mask = 0;
+			for (i = 0, zeros = 0; i < min(count, 8); i++) {
+				if (!(gpios & BIT(i)))
+					zeros++;
+				else if (!priv->rmi_led_mask)
+					priv->rmi_led_mask = BIT(i);
+			}
+			if (!priv->rmi_led_mask)
+				return -ENODEV;
+
+			priv->rmi_led_ctrl = ctrl + 4;
+			priv->rmi_led_brightness = ctrl + 7 + zeros;
+			return 0;
+		}
+	}
+
+	return -ENODEV;
+}
+
+/* Sets the LED. Leaves the touchpad in RMI mode. */
+static int __synaptics_rmi_led_set(struct psmouse *psmouse, bool on)
+{
+	struct synaptics_data *priv = psmouse->private;
+	u8 val;
+	int error;
+
+	error = synaptics_mode_cmd(psmouse, SYN_RMI_MODE);
+	if (error)
+		return error;
+
+	error = synaptics_rmi_write(psmouse, SYN_RMI_PAGE_SELECT, priv->rmi_led_page);
+	if (error)
+		return error;
+
+	if (on) {
+		error = synaptics_rmi_write(psmouse, priv->rmi_led_brightness,
+					    SYN_RMI_LED_BRIGHTNESS);
+		if (error)
+			return error;
+	}
+
+	error = synaptics_rmi_read(psmouse, priv->rmi_led_ctrl, &val);
+	if (error)
+		return error;
+
+	val = on ? val | priv->rmi_led_mask : val & ~priv->rmi_led_mask;
+	return synaptics_rmi_write(psmouse, priv->rmi_led_ctrl, val);
+}
+
+static int synaptics_set_mode(struct psmouse *psmouse);
+
+static int synaptics_rmi_led_set(struct led_classdev *led,
+				 enum led_brightness value)
+{
+	struct synaptics_data *priv = container_of(led, struct synaptics_data, rmi_led);
+	struct psmouse *psmouse = priv->psmouse;
+	int error, ret;
+
+	guard(mutex)(&priv->rmi_led_lock);
+
+	if (psmouse->state != PSMOUSE_ACTIVATED)
+		return -EBUSY;
+
+	error = psmouse_deactivate(psmouse);
+	if (error)
+		return error;
+
+	ret = __synaptics_rmi_led_set(psmouse, value != LED_OFF);
+
+	/* Setting the mode byte again leaves RMI access */
+	error = synaptics_set_mode(psmouse);
+	if (!ret)
+		ret = error;
+
+	error = psmouse_activate(psmouse);
+	return ret ?: error;
+}
+
+static void synaptics_rmi_led_init(struct psmouse *psmouse)
+{
+	struct synaptics_data *priv = psmouse->private;
+
+	if (!IS_REACHABLE(CONFIG_LEDS_CLASS) ||
+	    !psmouse_matches_pnp_id(psmouse, rmi_led_pnp_ids))
+		return;
+
+	if (synaptics_rmi_led_probe(psmouse))
+		return;
+
+	psmouse_info(psmouse, "touchpad LED on RMI F30 (page %u, ctrl %#x, mask %#x)\n",
+		     priv->rmi_led_page, priv->rmi_led_ctrl, priv->rmi_led_mask);
+	__synaptics_rmi_led_set(psmouse, false);
+	priv->has_rmi_led = true;
+}
+
+static void synaptics_rmi_led_register(struct psmouse *psmouse)
+{
+	struct synaptics_data *priv = psmouse->private;
+	int error;
+
+	if (!priv->has_rmi_led)
+		return;
+
+	mutex_init(&priv->rmi_led_lock);
+	priv->psmouse = psmouse;
+	priv->rmi_led.name = "synaptics::touchpad_disabled";
+	priv->rmi_led.max_brightness = 1;
+	priv->rmi_led.brightness_set_blocking = synaptics_rmi_led_set;
+	error = led_classdev_register(&psmouse->ps2dev.serio->dev, &priv->rmi_led);
+	if (error) {
+		psmouse_warn(psmouse, "failed to register touchpad LED: %d\n", error);
+		priv->has_rmi_led = false;
+	}
+}
+
 static int synaptics_set_mode(struct psmouse *psmouse)
 {
 	struct synaptics_data *priv = psmouse->private;
@@ -1444,6 +1674,9 @@ static void synaptics_disconnect(struct psmouse *psmouse)
 {
 	struct synaptics_data *priv = psmouse->private;
 
+	if (priv->has_rmi_led)
+		led_classdev_unregister(&priv->rmi_led);
+
 	/*
 	 * We might have left a breadcrumb when trying to
 	 * set up SMbus companion.
@@ -1496,6 +1729,10 @@ static int synaptics_reconnect(struct psmouse *psmouse)
 		return error;
 	}
 
+	/* The reset turned the LED off; the mode byte below leaves RMI access. */
+	if (priv->has_rmi_led && priv->rmi_led.brightness)
+		__synaptics_rmi_led_set(psmouse, true);
+
 	error = synaptics_set_mode(psmouse);
 	if (error) {
 		psmouse_err(psmouse, "Unable to initialize device.\n");
@@ -1616,6 +1853,8 @@ static int synaptics_init_ps2(struct psmouse *psmouse,
 	 */
 	priv->is_forcepad = psmouse_matches_pnp_id(psmouse, forcepad_pnp_ids);
 
+	synaptics_rmi_led_init(psmouse);
+
 	err = synaptics_set_mode(psmouse);
 	if (err) {
 		psmouse_err(psmouse, "Unable to initialize device.\n");
@@ -1693,6 +1932,8 @@ static int synaptics_init_ps2(struct psmouse *psmouse,
 		}
 	}
 
+	synaptics_rmi_led_register(psmouse);
+
 	return 0;
 
  init_fail:
diff --git a/drivers/input/mouse/synaptics.h b/drivers/input/mouse/synaptics.h
index 3853165b6..1d36a207e 100644
--- a/drivers/input/mouse/synaptics.h
+++ b/drivers/input/mouse/synaptics.h
@@ -6,6 +6,9 @@
 #ifndef _SYNAPTICS_H
 #define _SYNAPTICS_H
 
+#include <linux/leds.h>
+#include <linux/mutex.h>
+
 /* synaptics queries */
 #define SYN_QUE_IDENTIFY		0x00
 #define SYN_QUE_MODES			0x01
@@ -202,6 +205,16 @@ struct synaptics_data {
 	bool					press;
 	bool					report_press;
 	bool					is_forcepad;
+
+	/* Touchpad LED on RMI function $30, reached over PS/2 */
+	struct psmouse				*psmouse;
+	struct led_classdev			rmi_led;
+	struct mutex				rmi_led_lock;
+	bool					has_rmi_led;
+	u8					rmi_led_page;
+	u8					rmi_led_ctrl;
+	u8					rmi_led_mask;
+	u8					rmi_led_brightness;
 };
 
 void synaptics_module_init(void);
-- 
2.53.0