Re: [PATCH v11 14/18] HID: asus: expose XG Mobile identity and firmware information

diff --git a/drivers/hid/hid-asus.c b/drivers/hid/hid-asus.c
index e751bf1634349..f438cad13264a 100644
--- a/drivers/hid/hid-asus.c
+++ b/drivers/hid/hid-asus.c

@@ -6204,6 +6206,148 @@ static bool asus_xgm_is_supported_model(const struct asus_xgm_info *info)
 	return false;
 }
 
+/**
+ * asus_xgm_tlv_str() - Extract a "tag, length, data" field
+ * @dst: destination buffer
+ * @dst_len: size of @dst, including the trailing NUL
+ * @buf: answer of a version query
+ * @len: size of @buf
+ * @tag: three characters tag to look for
+ *
+ * The version query answers with an 8-byte binary blob followed by
+ * "tag, length, data" fields, where GEN holds the station generation and
+ * VER the firmware version.
+ *
+ * Return: 0 on success, -ENOENT if @tag is missing or its data does not
+ * fit @dst
+ */
+static int asus_xgm_tlv_str(char *dst, size_t dst_len, const u8 *buf,
+			    size_t len, const char *tag)
+{
+	size_t i;
+	u8 n;
+
+	for (i = 3; i + 4 <= len; i++) {
+		if (memcmp(buf + i, tag, 3))
+			continue;
+
+		n = buf[i + 3];
+		if (i + 4 + n > len || n >= dst_len)
+			return -ENOENT;
+
+		memcpy(dst, buf + i + 4, n);
+		dst[n] = '\0';
+
+		return 0;
+	}
+
+	return -ENOENT;
+}
+
+/**
+ * asus_xgm_get_version() - Query the firmware version of a station
+ * @hdev: HID device
+ * @info: identity structure whose generation and firmware_version fields
+ * get filled in
+ *
+ * Return: 0 on success, negative errno on failure
+ */
+static int asus_xgm_get_version(struct hid_device *hdev,
+				struct asus_xgm_info *info)
+{
+	size_t len = asus_report_len(hdev, FEATURE_KBD_LED_REPORT_ID2);
+	int ret;
+
+	if (!len)
+		return -EINVAL;
+
+	u8 *buf __free(kfree) = kzalloc(len, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	ret = asus_xgm_query(hdev, ASUS_XGM_QUERY_VERSION, buf, len);
+	if (ret < 0)
+		return ret;
+
+	if (len < 4 || buf[1] != ASUS_XGM_CMD_QUERY ||
+	    buf[2] != ASUS_XGM_QUERY_VERSION)
+		return -ENODEV;
+
+	asus_xgm_tlv_str(info->generation, sizeof(info->generation),
+			 buf, len, "GEN");
+	asus_xgm_tlv_str(info->firmware_version, sizeof(info->firmware_version),
+			 buf, len, "VER");
+
+	return 0;
+}