mt76: usb: use max packet length for m76u_copy

For transferring data over USB the optimal size is endpoint maxpacket.
For my hardware maxpaket for control endpoint is 64 bytes and changing
to this value from 128 bytes further shorten TBTT work time from
3ms to 1ms.
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>

drivers/net/wireless/mediatek/mt76/mt76.h

@@ -388,10 +388,9 @@ enum mt76u_out_ep {
 #define MCU_RESP_URB_SIZE	1024
 struct mt76_usb {
 	struct mutex usb_ctrl_mtx;
-	union {
-		u8 data[128];
-		__le32 reg_val;
-	};
+	__le32 reg_val;
+	u8 *data;
+	u16 data_len;
 
 	struct tasklet_struct rx_tasklet;
 	struct workqueue_struct *stat_wq;

drivers/net/wireless/mediatek/mt76/usb.c

@@ -163,7 +163,7 @@ static void mt76u_copy(struct mt76_dev *dev, u32 offset,
 
 	mutex_lock(&usb->usb_ctrl_mtx);
 	while (i < len) {
-		current_batch_size = min_t(int, sizeof(usb->data), len - i);
+		current_batch_size = min_t(int, usb->data_len, len - i);
 		memcpy(usb->data, val + i, current_batch_size);
 		ret = __mt76u_vendor_request(dev, MT_VEND_MULTI_WRITE,
 					     USB_DIR_OUT | USB_TYPE_VENDOR,
@@ -950,6 +950,15 @@ static const struct mt76_queue_ops usb_queue_ops = {
 	.kick = mt76u_tx_kick,
 };
 
+void mt76u_deinit(struct mt76_dev *dev)
+{
+	if (dev->usb.stat_wq) {
+		destroy_workqueue(dev->usb.stat_wq);
+		dev->usb.stat_wq = NULL;
+	}
+}
+EXPORT_SYMBOL_GPL(mt76u_deinit);
+
 int mt76u_init(struct mt76_dev *dev,
 	       struct usb_interface *intf)
 {
@@ -973,6 +982,15 @@ int mt76u_init(struct mt76_dev *dev,
 	if (!usb->stat_wq)
 		return -ENOMEM;
 
+	usb->data_len = usb_maxpacket(udev, usb_sndctrlpipe(udev, 0), 1);
+	if (usb->data_len < 32)
+		usb->data_len = 32;
+	usb->data = devm_kmalloc(dev->dev, usb->data_len, GFP_KERNEL);
+	if (!usb->data) {
+		mt76u_deinit(dev);
+		return -ENOMEM;
+	}
+
 	mutex_init(&usb->mcu.mutex);
 
 	mutex_init(&usb->usb_ctrl_mtx);
@@ -987,14 +1005,5 @@ int mt76u_init(struct mt76_dev *dev,
 }
 EXPORT_SYMBOL_GPL(mt76u_init);
 
-void mt76u_deinit(struct mt76_dev *dev)
-{
-	if (dev->usb.stat_wq) {
-		destroy_workqueue(dev->usb.stat_wq);
-		dev->usb.stat_wq = NULL;
-	}
-}
-EXPORT_SYMBOL_GPL(mt76u_deinit);
-
 MODULE_AUTHOR("Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>");
 MODULE_LICENSE("Dual BSD/GPL");