[PATCH v2 1/2] HID: lg-g15: add LCD contrast LED

[Torstein Eide <torsteine+linux@gmail.com>]

Wire values ({2, 32, 129, value}) match libg15's setLCDContrast()
byte-for-byte.

Tested on Logitech G15v2.

Based on libg15.c.

Signed-off-by: Torstein Eide <torsteine+linux@gmail.com>
Based-on-work-by: Philip Lawatsch <philip@lawatsch.at>
Based-on-work-by: Alex Ibrado <alex@ibrado.org>
Based-on-work-by: Anthony J. Mirabella <mirabeaj@gmail.com>
Based-on-work-by: Mike Lampard <mlampard@users.sourceforge.net>
Assisted-by: Claude:claude-sonnet-5
---
 drivers/hid/hid-lg-g15.c | 119 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 117 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hid-lg-g15.c b/drivers/hid/hid-lg-g15.c
index 02ef3e2094b4..3827c66ca3a9 100644
--- a/drivers/hid/hid-lg-g15.c
+++ b/drivers/hid/hid-lg-g15.c
@@ -59,7 +59,16 @@ enum lg_g15_led_type {
 	LG_G15_MACRO_PRESET2,
 	LG_G15_MACRO_PRESET3,
 	LG_G15_MACRO_RECORD,
-	LG_G15_LED_MAX
+	LG_G15_LED_MAX,
+	/*
+	 * LCD contrast uses a different feature-report sub-format than the
+	 * brightness/macro fields above (see lg_g15_contrast_set()) and has
+	 * no hardware readback, so it lives outside [0, LG_G15_LED_MAX) to
+	 * avoid being swept into the G13/macro loops bounded by
+	 * LG_G15_LED_MAX. G15/G15 v2 only; registered explicitly.
+	 */
+	LG_G15_LCD_CONTRAST = LG_G15_LED_MAX,
+	LG_G15_LED_ARRAY_SIZE
 };
 
 struct g13_input_report {
@@ -89,9 +98,10 @@ struct lg_g15_data {
 	struct input_dev *input_js; /* Separate joystick device for G13. */
 	struct hid_device *hdev;
 	enum lg_g15_model model;
-	struct lg_g15_led leds[LG_G15_LED_MAX];
+	struct lg_g15_led leds[LG_G15_LED_ARRAY_SIZE];
 	bool game_mode_enabled;
 	bool backlight_disabled;	/* true == HW backlight toggled *OFF* */
+	bool lcd_contrast_set;		/* LCD contrast written at least once */
 };
 
 /********* G13 LED functions ***********/
@@ -365,6 +375,69 @@ static int lg_g15_led_set(struct led_classdev *led_cdev,
 	return ret;
 }
 
+/*
+ * LCD contrast, report 2 field 32: {2, 32, 129, value}, value in
+ * {18, 22, 26} for low/medium/high. Distinct sub-format from the
+ * brightness/macro fields (value sits in byte 3, not byte 2, and byte 2 is
+ * a fixed marker rather than the field selector) and has no GET_REPORT
+ * readback, so brightness_get just returns the last value we set.
+ */
+/* Must be called with g15->mutex held */
+static int lg_g15_contrast_write(struct lg_g15_data *g15,
+				 enum led_brightness brightness)
+{
+	static const u8 contrast_values[] = { 18, 22, 26 };
+	int ret;
+
+	/*
+	 * The LED core does not clamp to max_brightness on every path (a
+	 * delayed set passes the raw sysfs value), so clamp here.
+	 */
+	brightness = min_t(enum led_brightness, brightness,
+			   ARRAY_SIZE(contrast_values) - 1);
+
+	g15->transfer_buf[0] = LG_G15_FEATURE_REPORT;
+	g15->transfer_buf[1] = 32;
+	g15->transfer_buf[2] = 129;
+	g15->transfer_buf[3] = contrast_values[brightness];
+
+	ret = hid_hw_raw_request(g15->hdev, LG_G15_FEATURE_REPORT,
+				 g15->transfer_buf, 4,
+				 HID_FEATURE_REPORT, HID_REQ_SET_REPORT);
+	if (ret != 4) {
+		hid_err(g15->hdev, "Error setting LCD contrast: %d\n", ret);
+		return (ret < 0) ? ret : -EIO;
+	}
+
+	g15->leds[LG_G15_LCD_CONTRAST].brightness = brightness;
+	g15->lcd_contrast_set = true;
+	return 0;
+}
+
+static int lg_g15_contrast_set(struct led_classdev *led_cdev,
+			       enum led_brightness brightness)
+{
+	struct lg_g15_data *g15 = dev_get_drvdata(led_cdev->dev->parent);
+	int ret;
+
+	if (led_cdev->flags & LED_UNREGISTERING)
+		return 0;
+
+	mutex_lock(&g15->mutex);
+	ret = lg_g15_contrast_write(g15, brightness);
+	mutex_unlock(&g15->mutex);
+
+	return ret;
+}
+
+static enum led_brightness lg_g15_contrast_get(struct led_classdev *led_cdev)
+{
+	struct lg_g15_led *g15_led =
+		container_of(led_cdev, struct lg_g15_led, cdev);
+
+	return g15_led->brightness;
+}
+
 static void lg_g15_leds_changed_work(struct work_struct *work)
 {
 	struct lg_g15_data *g15 = container_of(work, struct lg_g15_data, work);
@@ -1017,6 +1090,13 @@ static int lg_g15_register_led(struct lg_g15_data *g15, int i, const char *name)
 		break;
 	case LG_G15:
 	case LG_G15_V2:
+		if (i == LG_G15_LCD_CONTRAST) {
+			g15->leds[i].cdev.brightness_set_blocking = lg_g15_contrast_set;
+			g15->leds[i].cdev.brightness_get = lg_g15_contrast_get;
+			g15->leds[i].cdev.max_brightness = 2;
+			ret = devm_led_classdev_register(&g15->hdev->dev, &g15->leds[i].cdev);
+			break;
+		}
 		g15->leds[i].cdev.brightness_get = lg_g15_led_get;
 		fallthrough;
 	case LG_Z10:
@@ -1333,6 +1413,14 @@ static int lg_g15_probe(struct hid_device *hdev, const struct hid_device_id *id)
 			goto error_hw_stop;
 	}
 
+	/* The G11 shares the LG_G15 model but has no LCD */
+	if ((g15->model == LG_G15 && hdev->product != USB_DEVICE_ID_LOGITECH_G11) ||
+	    g15->model == LG_G15_V2) {
+		ret = lg_g15_register_led(g15, LG_G15_LCD_CONTRAST, "g15::lcd_contrast");
+		if (ret)
+			goto error_hw_stop;
+	}
+
 	return 0;
 
 error_hw_stop:
@@ -1389,12 +1477,39 @@ static void lg_g15_remove(struct hid_device *hdev)
 	hid_hw_stop(hdev);
 }
 
+/*
+ * The LCD does not retain its contrast across a USB reset or power loss;
+ * re-apply the last value userspace set, if any.
+ */
+static int lg_g15_resume(struct hid_device *hdev)
+{
+	struct lg_g15_data *g15 = hid_get_drvdata(hdev);
+	struct lg_g15_led *contrast;
+
+	if (!g15)
+		return 0;
+
+	contrast = &g15->leds[LG_G15_LCD_CONTRAST];
+	if (!contrast->cdev.dev)
+		return 0;
+
+	/* Under the mutex, so a concurrent contrast set cannot be undone */
+	mutex_lock(&g15->mutex);
+	if (g15->lcd_contrast_set)
+		lg_g15_contrast_write(g15, contrast->brightness);
+	mutex_unlock(&g15->mutex);
+
+	return 0;
+}
+
 static struct hid_driver lg_g15_driver = {
 	.name			= "lg-g15",
 	.id_table		= lg_g15_devices,
 	.raw_event		= lg_g15_raw_event,
 	.probe			= lg_g15_probe,
 	.remove			= lg_g15_remove,
+	.resume			= lg_g15_resume,
+	.reset_resume		= lg_g15_resume,
 };
 module_hid_driver(lg_g15_driver);
 
-- 
2.53.0