Limit USB transfers to the max size reported by the descriptors.

usbutils.c

@@ -305,7 +305,7 @@ static struct usb_find_devices find_dev[] = {
 		.epcount = 0,
 		.eps = NULL },
 #endif
-	{ DRV_LAST, NULL, 0, 0, 0, NULL, NULL, 0, 0, 0, 0, 0, 0, NULL }
+	{ DRV_LAST, NULL, 0, 0, 0, NULL, NULL, 0, 0, 0, 0, 0, 0, 0, NULL }
 };
 
 #ifdef USE_BFLSC
@@ -1647,6 +1647,7 @@ static int _usb_init(struct cgpu_info *cgpu, struct libusb_device *dev, struct u
 					&&  epdesc->wMaxPacketSize >= found->eps[k].size
 					&&  epdesc->bEndpointAddress == found->eps[k].ep) {
 						found->eps[k].found = true;
+						found->wMaxPacketSize = epdesc->wMaxPacketSize;
 						break;
 					}
 				}
@@ -2183,6 +2184,11 @@ usb_bulk_transfer(struct libusb_device_handle *dev_handle,
 {
 	int err, tries = 0;
 
+	/* Limit length of transfer to the largest this descriptor supports
+	 * and leave the higher level functions to transfer more if needed. */
+	if (length > cgpu->usbdev->found->wMaxPacketSize)
+		length = cgpu->usbdev->found->wMaxPacketSize;
+
 	cg_rlock(&cgusb_fd_lock);
 	err = libusb_bulk_transfer(dev_handle, endpoint, data, length,
 				   transferred, timeout);

usbutils.h

@@ -142,6 +142,7 @@ struct usb_find_devices {
 	int config;
 	int interface;
 	unsigned int timeout;
+	uint16_t wMaxPacketSize;
 	uint16_t latency;
 	int epcount;
 	struct usb_endpoints *eps;