Fix EFI net issues

Fixes the following issues found when testing
EFI_SIMPLE_NETWORK_PROTOCOL on cuttlefish:

1. EFI uses the first net device by default. Cuttlefish creates 3
   network devices but the first one doesn't have an assigned MAC. This
   causes failure when EFI registers network device. The solution is to
   call `eth_set_current()` first to scan and select a different one.
2. Virtio net stops receiving when rx ring runs out of buffer. Adding
   back buffer is not sufficient to resume it. A notification is
   necessary to kick if off again.

TEST: Tested Fastboot over TCP in GBL UEFI app.
Change-Id: I73a59cf188fb45212a4666f46b88fdf55de9d663

2 files changed, 12 insertions, 0 deletions

diff --git a/drivers/virtio/virtio_net.c b/drivers/virtio/virtio_net.c
index 1794f73a8d..69c7d5abb9 100644
--- a/drivers/virtio/virtio_net.c
+++ b/drivers/virtio/virtio_net.c
@@ -127,9 +127,18 @@ static int virtio_net_free_pkt(struct udevice *dev, uchar *packet, int length)
 	struct virtio_sg sg = { buf, VIRTIO_NET_RX_BUF_SIZE };
 	struct virtio_sg *sgs[] = { &sg };
 
+	// virtio_net stops receiving frames once it completely runs out of rx ring
+	// buffers. Adding back buffers does not resume it. An explicit
+	// notification is necessary to kick it off again.
+	bool need_notify = priv->rx_vq->free_head == 0;
+
 	/* Put the buffer back to the rx ring */
 	virtqueue_add(priv->rx_vq, sgs, 0, 1);
 
+	if (need_notify) {
+		virtqueue_kick(priv->rx_vq);
+	}
+
 	return 0;
 }
 
diff --git a/lib/efi_loader/efi_net.c b/lib/efi_loader/efi_net.c
index 96a5bcca27..580ec3d29f 100644
--- a/lib/efi_loader/efi_net.c
+++ b/lib/efi_loader/efi_net.c
@@ -863,6 +863,9 @@ efi_status_t efi_net_register(void)
 	efi_status_t r;
 	int i;
 
+	// Cuttlefish has multiple network devices. Call `eth_set_current()` to
+	// scan and select a working one.
+	eth_set_current();
 	if (!eth_get_dev()) {
 		/* No network device active, don't expose any */
 		return EFI_SUCCESS;