dm: eth: Provide a way for drivers to manage packet buffers

Some drivers need a chance to manage their receive buffers after the
packet has been handled by the network stack. Add an operation that
will allow the driver to be called in that case.

Reported-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
Tested-on: pcduino3

include/net.h

@@ -97,7 +97,12 @@ struct eth_pdata {
  * send: Send the bytes passed in "packet" as a packet on the wire
  * recv: Check if the hardware received a packet. If so, set the pointer to the
  *	 packet buffer in the packetp parameter. If not, return an error or 0 to
- *	 indicate that the hardware receive FIFO is empty
+ *	 indicate that the hardware receive FIFO is empty. If 0 is returned, the
+ *	 network stack will not process the empty packet, but free_pkt() will be
+ *	 called if supplied
+ * free_pkt: Give the driver an opportunity to manage its packet buffer memory
+ *	     when the network stack is finished processing it. This will only be
+ *	     called when no error was returned from recv - optional
  * stop: Stop the hardware from looking for packets - may be called even if
  *	 state == PASSIVE
  * mcast: Join or leave a multicast group (for TFTP) - optional
@@ -113,6 +118,7 @@ struct eth_ops {
 	int (*start)(struct udevice *dev);
 	int (*send)(struct udevice *dev, void *packet, int length);
 	int (*recv)(struct udevice *dev, uchar **packetp);
+	int (*free_pkt)(struct udevice *dev, uchar *packet, int length);
 	void (*stop)(struct udevice *dev);
 #ifdef CONFIG_MCAST_TFTP
 	int (*mcast)(struct udevice *dev, const u8 *enetaddr, int join);

net/eth.c

@@ -344,7 +344,9 @@ int eth_rx(void)
 		ret = eth_get_ops(current)->recv(current, &packet);
 		if (ret > 0)
 			net_process_received_packet(packet, ret);
-		else
+		if (ret >= 0 && eth_get_ops(current)->free_pkt)
+			eth_get_ops(current)->free_pkt(current, packet, ret);
+		if (ret <= 0)
 			break;
 	}
 	if (ret == -EAGAIN)