[PATCH v4 01/11] HID: asus: refactor init sequence per spec

[Antheas Kapenekakis <lkml@antheas.dev>]

Currently, asus_kbd_init() uses a reverse engineered init sequence
from Windows, which contains the handshakes from multiple programs.
Keep the main one, which is 0x5a (meant for brightness drivers).

In addition, perform a get_response and check if the response is the
same. To avoid regressions, print an error if the response does not
match instead of rejecting device.

Then, refactor asus_kbd_get_functions() to use the same ID it is called
with, instead of hardcoding it to 0x5a so that it may be used for 0x0d
in the future.

Signed-off-by: Antheas Kapenekakis <lkml@antheas.dev>
---
 drivers/hid/hid-asus.c | 82 +++++++++++++++++++++++-------------------
 1 file changed, 46 insertions(+), 36 deletions(-)

diff --git a/drivers/hid/hid-asus.c b/drivers/hid/hid-asus.c
index 46e3e42f9eb5f..8d4df1b6f143b 100644
--- a/drivers/hid/hid-asus.c
+++ b/drivers/hid/hid-asus.c
@@ -48,7 +48,7 @@ MODULE_DESCRIPTION("Asus HID Keyboard and TouchPad");
 #define FEATURE_REPORT_ID 0x0d
 #define INPUT_REPORT_ID 0x5d
 #define FEATURE_KBD_REPORT_ID 0x5a
-#define FEATURE_KBD_REPORT_SIZE 16
+#define FEATURE_KBD_REPORT_SIZE 64
 #define FEATURE_KBD_LED_REPORT_ID1 0x5d
 #define FEATURE_KBD_LED_REPORT_ID2 0x5e
 
@@ -388,14 +388,41 @@ static int asus_kbd_set_report(struct hid_device *hdev, const u8 *buf, size_t bu
 
 static int asus_kbd_init(struct hid_device *hdev, u8 report_id)
 {
-	const u8 buf[] = { report_id, 0x41, 0x53, 0x55, 0x53, 0x20, 0x54,
-		     0x65, 0x63, 0x68, 0x2e, 0x49, 0x6e, 0x63, 0x2e, 0x00 };
+	/*
+	 * Asus handshake identifying us as a driver (0x5A)
+	 * 0x5A then ASCII for "ASUS Tech.Inc."
+	 * 0x5D is for userspace Windows applications.
+	 *
+	 * The handshake is first sent as a set_report, then retrieved
+	 * from a get_report to verify the response.
+	 */
+	const u8 buf[] = { report_id, 0x41, 0x53, 0x55, 0x53, 0x20,
+		0x54, 0x65, 0x63, 0x68, 0x2e, 0x49, 0x6e, 0x63, 0x2e, 0x00 };
+	u8 *readbuf;
 	int ret;
 
 	ret = asus_kbd_set_report(hdev, buf, sizeof(buf));
-	if (ret < 0)
-		hid_err(hdev, "Asus failed to send init command: %d\n", ret);
+	if (ret < 0) {
+		hid_err(hdev, "Asus failed to send handshake: %d\n", ret);
+		return ret;
+	}
 
+	readbuf = kzalloc(FEATURE_KBD_REPORT_SIZE, GFP_KERNEL);
+	if (!readbuf)
+		return -ENOMEM;
+
+	ret = hid_hw_raw_request(hdev, report_id, readbuf,
+				 FEATURE_KBD_REPORT_SIZE, HID_FEATURE_REPORT,
+				 HID_REQ_GET_REPORT);
+	if (ret < 0) {
+		hid_err(hdev, "Asus failed to receive handshake ack: %d\n", ret);
+	} else if (memcmp(readbuf, buf, sizeof(buf)) != 0) {
+		hid_err(hdev, "Asus handshake returned invalid response: %*ph\n",
+			FEATURE_KBD_REPORT_SIZE, readbuf);
+		// Do not return error if handshake is wrong to avoid regressions
+	}
+
+	kfree(readbuf);
 	return ret;
 }
 
@@ -417,7 +444,7 @@ static int asus_kbd_get_functions(struct hid_device *hdev,
 	if (!readbuf)
 		return -ENOMEM;
 
-	ret = hid_hw_raw_request(hdev, FEATURE_KBD_REPORT_ID, readbuf,
+	ret = hid_hw_raw_request(hdev, report_id, readbuf,
 				 FEATURE_KBD_REPORT_SIZE, HID_FEATURE_REPORT,
 				 HID_REQ_GET_REPORT);
 	if (ret < 0) {
@@ -540,42 +567,25 @@ static int asus_kbd_register_leds(struct hid_device *hdev)
 	unsigned char kbd_func;
 	int ret;
 
-	if (drvdata->quirks & QUIRK_ROG_NKEY_KEYBOARD) {
-		/* Initialize keyboard */
-		ret = asus_kbd_init(hdev, FEATURE_KBD_REPORT_ID);
-		if (ret < 0)
-			return ret;
-
-		/* The LED endpoint is initialised in two HID */
-		ret = asus_kbd_init(hdev, FEATURE_KBD_LED_REPORT_ID1);
-		if (ret < 0)
-			return ret;
-
-		ret = asus_kbd_init(hdev, FEATURE_KBD_LED_REPORT_ID2);
-		if (ret < 0)
-			return ret;
+	ret = asus_kbd_init(hdev, FEATURE_KBD_REPORT_ID);
+	if (ret < 0)
+		return ret;
 
-		if (dmi_match(DMI_PRODUCT_FAMILY, "ProArt P16")) {
-			ret = asus_kbd_disable_oobe(hdev);
-			if (ret < 0)
-				return ret;
-		}
-	} else {
-		/* Initialize keyboard */
-		ret = asus_kbd_init(hdev, FEATURE_KBD_REPORT_ID);
-		if (ret < 0)
-			return ret;
+	/* Get keyboard functions */
+	ret = asus_kbd_get_functions(hdev, &kbd_func, FEATURE_KBD_REPORT_ID);
+	if (ret < 0)
+		return ret;
 
-		/* Get keyboard functions */
-		ret = asus_kbd_get_functions(hdev, &kbd_func, FEATURE_KBD_REPORT_ID);
+	if (dmi_match(DMI_PRODUCT_FAMILY, "ProArt P16")) {
+		ret = asus_kbd_disable_oobe(hdev);
 		if (ret < 0)
 			return ret;
-
-		/* Check for backlight support */
-		if (!(kbd_func & SUPPORT_KBD_BACKLIGHT))
-			return -ENODEV;
 	}
 
+	/* Check for backlight support */
+	if (!(kbd_func & SUPPORT_KBD_BACKLIGHT))
+		return -ENODEV;
+
 	drvdata->kbd_backlight = devm_kzalloc(&hdev->dev,
 					      sizeof(struct asus_kbd_leds),
 					      GFP_KERNEL);
-- 
2.49.0