gs_usb.h: introduce CAN-FD support

The CANtact FD and other devices implement a gs-usb compatible USB
protocol. The protocol has been extended to support CAN-FD and the
changes on the Linux gs_usb driver will be mainlined soon.

This patch adds the new GS_CAN_MODE_*, GS_CAN_FEATURE_* and
GS_CAN_FLAG_* bits as well as struct gs_host_frame_canfd to the
candlelight driver.

This is mainly for documentation purpose, as the STM32F042 and
STM32F072 don't support CAN-FD. But there are some ports to CAN-FD
capable STM32 µC that can make use of these definitions.

[1] linklayer/gs_usb_fd#2

include/gs_usb.h

@@ -42,6 +42,7 @@ THE SOFTWARE.
 /* #define GS_CAN_FEATURE_IDENTIFY              (1<<5) */
 /* #define GS_CAN_FEATURE_USER_ID               (1<<6) */
 #define GS_CAN_MODE_PAD_PKTS_TO_MAX_PKT_SIZE    (1<<7)
+#define GS_CAN_MODE_FD                          (1<<8)
 
 #define GS_CAN_FEATURE_LISTEN_ONLY              (1<<0)
 #define GS_CAN_FEATURE_LOOP_BACK                (1<<1)
@@ -50,10 +51,13 @@ THE SOFTWARE.
 #define GS_CAN_FEATURE_HW_TIMESTAMP             (1<<4)
 #define GS_CAN_FEATURE_IDENTIFY                 (1<<5)
 #define GS_CAN_FEATURE_USER_ID                  (1<<6)
-
 #define GS_CAN_FEATURE_PAD_PKTS_TO_MAX_PKT_SIZE (1<<7)
+#define GS_CAN_FEATURE_FD                       (1<<8)
 
-#define GS_CAN_FLAG_OVERFLOW 1
+#define GS_CAN_FLAG_OVERFLOW                    (1<<0)
+#define GS_CAN_FLAG_FD                          (1<<1)
+#define GS_CAN_FLAG_BRS                         (1<<2)
+#define GS_CAN_FLAG_ESI                         (1<<3)
 
 #define CAN_EFF_FLAG 0x80000000U /* EFF/SFF is set in the MSB */
 #define CAN_RTR_FLAG 0x40000000U /* remote transmission request */
@@ -229,6 +233,18 @@ struct gs_host_frame {
 
 } __packed;
 
+struct gs_host_frame_canfd {
+	u32 echo_id;
+	u32 can_id;
+
+	u8 can_dlc;
+	u8 channel;
+	u8 flags;
+	u8 reserved;
+
+	u8 data[64];
+} __packed;
+
 struct gs_tx_context {
 	struct gs_can *dev;
 	unsigned int echo_id;