can: gs_usb: use union and FLEX_ARRAY for data in struct gs_host_frame

Modify struct gs_host_frame to make use of a union and
DECLARE_FLEX_ARRAY to be able to store different data (lengths), which
will be added in later commits.

Store the gs_host_frame length in TX direction (host -> device) in
struct gs_can::hf_size_tx and RX direction (device -> host) in struct
gs_usb::hf_size_rx so it must be calculated only once.

Link: https://lore.kernel.org/all/20220309124132.291861-15-mkl@pengutronix.de
Signed-off-by: Peter Fink <pfink@christ-es.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/gs_usb.c

@@ -146,6 +146,10 @@ struct gs_device_bt_const {
 
 #define GS_CAN_FLAG_OVERFLOW BIT(0)
 
+struct classic_can {
+	u8 data[8];
+} __packed;
+
 struct gs_host_frame {
 	u32 echo_id;
 	__le32 can_id;
@@ -155,7 +159,9 @@ struct gs_host_frame {
 	u8 flags;
 	u8 reserved;
 
-	u8 data[8];
+	union {
+		DECLARE_FLEX_ARRAY(struct classic_can, classic_can);
+	};
 } __packed;
 /* The GS USB devices make use of the same flags and masks as in
  * linux/can.h and linux/can/error.h, and no additional mapping is necessary.
@@ -187,6 +193,8 @@ struct gs_can {
 	struct can_bittiming_const bt_const;
 	unsigned int channel;	/* channel number */
 
+	unsigned int hf_size_tx;
+
 	/* This lock prevents a race condition between xmit and receive. */
 	spinlock_t tx_ctx_lock;
 	struct gs_tx_context tx_context[GS_MAX_TX_URBS];
@@ -200,6 +208,7 @@ struct gs_usb {
 	struct gs_can *canch[GS_MAX_INTF];
 	struct usb_anchor rx_submitted;
 	struct usb_device *udev;
+	unsigned int hf_size_rx;
 	u8 active_channels;
 };
 
@@ -343,7 +352,7 @@ static void gs_usb_receive_bulk_callback(struct urb *urb)
 		cf->can_id = le32_to_cpu(hf->can_id);
 
 		can_frame_set_cc_len(cf, hf->can_dlc, dev->can.ctrlmode);
-		memcpy(cf->data, hf->data, 8);
+		memcpy(cf->data, hf->classic_can->data, 8);
 
 		/* ERROR frames tell us information about the controller */
 		if (le32_to_cpu(hf->can_id) & CAN_ERR_FLAG)
@@ -398,7 +407,7 @@ static void gs_usb_receive_bulk_callback(struct urb *urb)
  resubmit_urb:
 	usb_fill_bulk_urb(urb, usbcan->udev,
 			  usb_rcvbulkpipe(usbcan->udev, GSUSB_ENDPOINT_IN),
-			  hf, sizeof(struct gs_host_frame),
+			  hf, dev->parent->hf_size_rx,
 			  gs_usb_receive_bulk_callback, usbcan);
 
 	rc = usb_submit_urb(urb, GFP_ATOMIC);
@@ -485,7 +494,7 @@ static netdev_tx_t gs_can_start_xmit(struct sk_buff *skb,
 	if (!urb)
 		goto nomem_urb;
 
-	hf = usb_alloc_coherent(dev->udev, sizeof(*hf), GFP_ATOMIC,
+	hf = usb_alloc_coherent(dev->udev, dev->hf_size_tx, GFP_ATOMIC,
 				&urb->transfer_dma);
 	if (!hf) {
 		netdev_err(netdev, "No memory left for USB buffer\n");
@@ -509,11 +518,11 @@ static netdev_tx_t gs_can_start_xmit(struct sk_buff *skb,
 	hf->can_id = cpu_to_le32(cf->can_id);
 	hf->can_dlc = can_get_cc_dlc(cf, dev->can.ctrlmode);
 
-	memcpy(hf->data, cf->data, cf->len);
+	memcpy(hf->classic_can->data, cf->data, cf->len);
 
 	usb_fill_bulk_urb(urb, dev->udev,
 			  usb_sndbulkpipe(dev->udev, GSUSB_ENDPOINT_OUT),
-			  hf, sizeof(*hf),
+			  hf, dev->hf_size_tx,
 			  gs_usb_xmit_callback, txc);
 
 	urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
@@ -531,8 +540,8 @@ static netdev_tx_t gs_can_start_xmit(struct sk_buff *skb,
 		gs_free_tx_context(txc);
 
 		usb_unanchor_urb(urb);
-		usb_free_coherent(dev->udev,
-				  sizeof(*hf), hf, urb->transfer_dma);
+		usb_free_coherent(dev->udev, urb->transfer_buffer_length,
+				  urb->transfer_buffer, urb->transfer_dma);
 
 		if (rc == -ENODEV) {
 			netif_device_detach(netdev);
@@ -552,7 +561,8 @@ static netdev_tx_t gs_can_start_xmit(struct sk_buff *skb,
 	return NETDEV_TX_OK;
 
  badidx:
-	usb_free_coherent(dev->udev, sizeof(*hf), hf, urb->transfer_dma);
+	usb_free_coherent(dev->udev, urb->transfer_buffer_length,
+			  urb->transfer_buffer, urb->transfer_dma);
  nomem_hf:
 	usb_free_urb(urb);
 
@@ -569,13 +579,16 @@ static int gs_can_open(struct net_device *netdev)
 	struct gs_usb *parent = dev->parent;
 	int rc, i;
 	struct gs_device_mode *dm;
+	struct gs_host_frame *hf;
 	u32 ctrlmode;
 	u32 flags = 0;
 
 	rc = open_candev(netdev);
 	if (rc)
 		return rc;
 
+	dev->hf_size_tx = struct_size(hf, classic_can, 1);
+
 	if (!parent->active_channels) {
 		for (i = 0; i < GS_MAX_RX_URBS; i++) {
 			struct urb *urb;
@@ -588,7 +601,7 @@ static int gs_can_open(struct net_device *netdev)
 
 			/* alloc rx buffer */
 			buf = usb_alloc_coherent(dev->udev,
-						 sizeof(struct gs_host_frame),
+						 dev->parent->hf_size_rx,
 						 GFP_KERNEL,
 						 &urb->transfer_dma);
 			if (!buf) {
@@ -604,7 +617,7 @@ static int gs_can_open(struct net_device *netdev)
 					  usb_rcvbulkpipe(dev->udev,
 							  GSUSB_ENDPOINT_IN),
 					  buf,
-					  sizeof(struct gs_host_frame),
+					  dev->parent->hf_size_rx,
 					  gs_usb_receive_bulk_callback, parent);
 			urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
 
@@ -886,6 +899,7 @@ static int gs_usb_probe(struct usb_interface *intf,
 			const struct usb_device_id *id)
 {
 	struct usb_device *udev = interface_to_usbdev(intf);
+	struct gs_host_frame *hf;
 	struct gs_usb *dev;
 	int rc = -ENOMEM;
 	unsigned int icount, i;
@@ -947,6 +961,7 @@ static int gs_usb_probe(struct usb_interface *intf,
 	}
 
 	init_usb_anchor(&dev->rx_submitted);
+	dev->hf_size_rx = struct_size(hf, classic_can, 1);
 
 	usb_set_intfdata(intf, dev);
 	dev->udev = udev;