feat(usb): Add boot protocol support

* USB boot protocol support
* Use a single definition of a boot report, used for regular reports in
  non-6KRO, and for rollover in all branches.
* Handle gaps in the zmk report when producing a boot report in HKRO mode. For
  .example, if it was 8KRO, it would be possible to have the state 0 0 0 0 0 0 0
  17 (by pressing 8 keys, and letting go of the first 7). Copying the first 6
  bytes would not show up the single pressed key.
* Disable usb status change and callback on SOF events:
  SOF events were introduced by the boot protocol changes, and required internally
  by Zephyr's idle support, but are unused within ZMK itself. Ignore them in the
  usb status callback.

---------

Co-authored-by: Andrew Childs <lorne@cons.org.nz>

app/src/usb_hid.c

@@ -23,11 +23,75 @@ static K_SEM_DEFINE(hid_sem, 1, 1);
 
 static void in_ready_cb(const struct device *dev) { k_sem_give(&hid_sem); }
 
+#define HID_GET_REPORT_TYPE_MASK 0xff00
+#define HID_GET_REPORT_ID_MASK 0x00ff
+
+#define HID_REPORT_TYPE_INPUT 0x100
+#define HID_REPORT_TYPE_OUTPUT 0x200
+#define HID_REPORT_TYPE_FEATURE 0x300
+
+#if IS_ENABLED(CONFIG_ZMK_USB_BOOT)
+static uint8_t hid_protocol = HID_PROTOCOL_REPORT;
+
+static void set_proto_cb(const struct device *dev, uint8_t protocol) { hid_protocol = protocol; }
+
+void zmk_usb_hid_set_protocol(uint8_t protocol) { hid_protocol = protocol; }
+#endif /* IS_ENABLED(CONFIG_ZMK_USB_BOOT) */
+
+static uint8_t *get_keyboard_report(size_t *len) {
+    if (hid_protocol == HID_PROTOCOL_REPORT) {
+        struct zmk_hid_keyboard_report *report = zmk_hid_get_keyboard_report();
+        *len = sizeof(*report);
+        return (uint8_t *)report;
+    }
+#if IS_ENABLED(CONFIG_ZMK_USB_BOOT)
+    zmk_hid_boot_report_t *boot_report = zmk_hid_get_boot_report();
+    *len = sizeof(*boot_report);
+    return (uint8_t *)boot_report;
+#endif
+}
+
+static int get_report_cb(const struct device *dev, struct usb_setup_packet *setup, int32_t *len,
+                         uint8_t **data) {
+
+    /*
+     * 7.2.1 of the HID v1.11 spec is unclear about handling requests for reports that do not exist
+     * For requested reports that aren't input reports, return -ENOTSUP like the Zephyr subsys does
+     */
+    if ((setup->wValue & HID_GET_REPORT_TYPE_MASK) != HID_REPORT_TYPE_INPUT) {
+        LOG_ERR("Unsupported report type %d requested", (setup->wValue & HID_GET_REPORT_TYPE_MASK)
+                                                            << 8);
+        return -ENOTSUP;
+    }
+
+    switch (setup->wValue & HID_GET_REPORT_ID_MASK) {
+    case ZMK_HID_REPORT_ID_KEYBOARD: {
+        *data = get_keyboard_report(len);
+        break;
+    }
+    case ZMK_HID_REPORT_ID_CONSUMER: {
+        struct zmk_hid_consumer_report *report = zmk_hid_get_consumer_report();
+        *data = (uint8_t *)report;
+        *len = sizeof(*report);
+        break;
+    }
+    default:
+        LOG_ERR("Invalid report ID %d requested", setup->wValue & HID_GET_REPORT_ID_MASK);
+        return -EINVAL;
+    }
+
+    return 0;
+}
+
 static const struct hid_ops ops = {
+#if IS_ENABLED(CONFIG_ZMK_USB_BOOT)
+    .protocol_change = set_proto_cb,
+#endif
     .int_in_ready = in_ready_cb,
+    .get_report = get_report_cb,
 };
 
-int zmk_usb_hid_send_report(const uint8_t *report, size_t len) {
+static int zmk_usb_hid_send_report(const uint8_t *report, size_t len) {
     switch (zmk_usb_get_status()) {
     case USB_DC_SUSPEND:
         return usb_wakeup_request();
@@ -48,6 +112,23 @@ int zmk_usb_hid_send_report(const uint8_t *report, size_t len) {
     }
 }
 
+int zmk_usb_hid_send_keyboard_report() {
+    size_t len;
+    uint8_t *report = get_keyboard_report(&len);
+    return zmk_usb_hid_send_report(report, len);
+}
+
+int zmk_usb_hid_send_consumer_report() {
+#if IS_ENABLED(CONFIG_ZMK_USB_BOOT)
+    if (hid_protocol == HID_PROTOCOL_BOOT) {
+        return -ENOTSUP;
+    }
+#endif /* IS_ENABLED(CONFIG_ZMK_USB_BOOT) */
+
+    struct zmk_hid_consumer_report *report = zmk_hid_get_consumer_report();
+    return zmk_usb_hid_send_report((uint8_t *)report, sizeof(*report));
+}
+
 static int zmk_usb_hid_init(const struct device *_arg) {
     hid_dev = device_get_binding("HID_0");
     if (hid_dev == NULL) {
@@ -56,6 +137,11 @@ static int zmk_usb_hid_init(const struct device *_arg) {
     }
 
     usb_hid_register_device(hid_dev, zmk_hid_report_desc, sizeof(zmk_hid_report_desc), &ops);
+
+#if IS_ENABLED(CONFIG_ZMK_USB_BOOT)
+    usb_hid_set_proto_code(hid_dev, HID_BOOT_IFACE_CODE_KEYBOARD);
+#endif /* IS_ENABLED(CONFIG_ZMK_USB_BOOT) */
+
     usb_hid_init(hid_dev);
 
     return 0;