usb: allow hardware to handle ZLP for Variable-length Data Stage

Allow hardware to handle ZLP for Variable-length Data Stage.

Signed-off-by: Johann Fischer <j.fischer@phytec.de>

drivers/usb/device/Kconfig

@@ -61,6 +61,7 @@ menuconfig USB_NRF52840
 	depends on SOC_NRF52840
 	select USB_DEVICE_DRIVER
 	select NRFX_USBD
+	select USB_DEVICE_DISABLE_ZLP_EPIN_HANDLING
 	help
 	  nRF52840 USB Device Controller Driver
 

subsys/usb/Kconfig

@@ -79,6 +79,12 @@ config USB_DEVICE_REMOTE_WAKEUP
 	help
 	  This option requires USBD peripheral driver to also support remote wakeup.
 
+config USB_DEVICE_DISABLE_ZLP_EPIN_HANDLING
+	bool
+	help
+	  Stack should not handle ZLP for Variable-length Data Stage
+	  bacause it is taken over by the hardware.
+
 config USB_DEVICE_BOS
 	bool "Enable USB Binary Device Object Store (BOS)"
 

subsys/usb/usb_device.c

@@ -245,6 +245,7 @@ static void usb_data_to_host(u16_t len)
 		usb_dev.data_buf += chunk;
 		usb_dev.data_buf_residue -= chunk;
 
+#ifndef CONFIG_USB_DEVICE_DISABLE_ZLP_EPIN_HANDLING
 		/*
 		 * Set ZLP flag when host asks for a bigger length and the
 		 * last chunk is wMaxPacketSize long, to indicate the last
@@ -259,6 +260,7 @@ static void usb_data_to_host(u16_t len)
 				usb_dev.zlp_flag = true;
 			}
 		}
+#endif
 
 	} else {
 		usb_dev.zlp_flag = false;