net: bcmgenet: set RBUF_SKIP_FCS based on UniMAC CRC forwarding

When the UniMAC block is configured to forward the CRC as part of the
Ethernet frame (priv->crc_fwd_en, set by default), enabling the hardware
RX checksum block unveiled that the dma_rxchk_bit was never set in the
per-packet status bits (dma_flag in bcmgenet_desc_rx). This would make
the chksum_ok variable to be never set to 1, and the networking stack
would have to compute the packet checksums, which takes a substantial
amount of time.

In order for the RXCHK block to properly compute the packet checksum in
hardware, we also need to set the RBUF_SKIP_FCS bit accordingly.
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/broadcom/genet/bcmgenet.c

@@ -416,6 +416,15 @@ static int bcmgenet_set_rx_csum(struct net_device *dev,
 	else
 		rbuf_chk_ctrl &= ~RBUF_RXCHK_EN;
 	priv->desc_rxchk_en = rx_csum_en;
+
+	/* If UniMAC forwards CRC, we need to skip over it to get
+	 * a valid CHK bit to be set in the per-packet status word
+	*/
+	if (rx_csum_en && priv->crc_fwd_en)
+		rbuf_chk_ctrl |= RBUF_SKIP_FCS;
+	else
+		rbuf_chk_ctrl &= ~RBUF_SKIP_FCS;
+
 	bcmgenet_rbuf_writel(priv, rbuf_chk_ctrl, RBUF_CHK_CTRL);
 
 	return 0;