slicemk: usb hid: use queue for sending data (2024-04-22)

app/Kconfig.slicemk

@@ -17,3 +17,6 @@ config ZMK_SPLIT_CENTRAL_SPLIT_RUN_STACK_SIZE
 # included in ZMK by default. for now this makes sense.
 config ZMK_MOUSE
     default y
+
+config ZMK_LOW_PRIORITY_WORK_QUEUE
+    default y

app/src/usb_hid.c

@@ -17,14 +17,51 @@
 #include <zmk/hid_indicators.h>
 #endif // IS_ENABLED(CONFIG_ZMK_HID_INDICATORS)
 #include <zmk/event_manager.h>
+#include <zmk/workqueue.h>
 
 LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
 
 static const struct device *hid_dev;
 
-static K_SEM_DEFINE(hid_sem, 1, 1);
+struct usb_hid_msg {
+	uint8_t data[CONFIG_HID_INTERRUPT_EP_MPS];
+	uint8_t len;
+};
+
+// Keep track of the number of consecutive HID writes failures so messages can
+// be dropped if they continuously fail to send.
+static int usb_hid_failed;
+
+K_MSGQ_DEFINE(usb_hid_msgq, sizeof(struct usb_hid_msg), 8, 1);
+
+static void usb_hid_work_handler(struct k_work *work) {
+	struct usb_hid_msg msg;
+	while (k_msgq_peek(&usb_hid_msgq, &msg) == 0) {
+		// Attempt to write HID message. If it fails, retry with up to a total
+		// of three attempts. Reattempt after 10ms or when the USB HID interrupt
+		// IN endpoint is ready, whichever comes first.
+		int err = hid_int_ep_write(hid_dev, msg.data, msg.len, NULL);
+		if (err) {
+			usb_hid_failed++;
+			if (usb_hid_failed < 3) {
+				k_work_reschedule_for_queue(zmk_workqueue_lowprio_work_q(), k_work_delayable_from_work(work), K_MSEC(10));
+				return;
+			} else {
+				LOG_ERR("dropped HID message due to %d consecutive failures", usb_hid_failed);
+			}
+		}
+
+		// Remove message from message queue and reset failure count.
+		k_msgq_get(&usb_hid_msgq, &msg, K_NO_WAIT);
+		usb_hid_failed = 0;
+	}
+}
+
+K_WORK_DELAYABLE_DEFINE(usb_hid_work, usb_hid_work_handler);
 
-static void in_ready_cb(const struct device *dev) { k_sem_give(&hid_sem); }
+static void in_ready_cb(const struct device *dev) {
+	k_work_reschedule_for_queue(zmk_workqueue_lowprio_work_q(), &usb_hid_work, K_NO_WAIT);
+}
 
 #define HID_GET_REPORT_TYPE_MASK 0xff00
 #define HID_GET_REPORT_ID_MASK 0x00ff
@@ -136,14 +173,19 @@ static int zmk_usb_hid_send_report(const uint8_t *report, size_t len) {
     case USB_DC_UNKNOWN:
         return -ENODEV;
     default:
-        k_sem_take(&hid_sem, K_MSEC(30));
-        int err = hid_int_ep_write(hid_dev, report, len, NULL);
-
-        if (err) {
-            k_sem_give(&hid_sem);
-        }
-
-        return err;
+		{
+			struct usb_hid_msg msg = {.len = len};
+			memcpy(&msg.data, report, len);
+			if (k_msgq_put(&usb_hid_msgq, &msg, K_NO_WAIT)) {
+				LOG_ERR("failed to add HID message to queue");
+			} else {
+				// Add to queue. This uses "schedule" rather than "reschedule"
+				// to keep the existing delay if the work item is already in the
+				// queue such as following a USB HID write failure.
+				k_work_schedule_for_queue(zmk_workqueue_lowprio_work_q(), &usb_hid_work, K_NO_WAIT);
+			}
+			return 0;
+		}
     }
 }