net: sh_eth: fix incorrect RX length error if R8A7740

This patch fixes an issue that the driver increments the "RX length error"
on every buffer in sh_eth_rx() if the R8A7740.
This patch also adds a description about the Receive Frame Status bits.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 4 deletions

diff --git a/drivers/net/ethernet/renesas/sh_eth.c b/drivers/net/ethernet/renesas/sh_eth.c
index b4479b5aaee4..5e3982fc5398 100644
--- a/drivers/net/ethernet/renesas/sh_eth.c
+++ b/drivers/net/ethernet/renesas/sh_eth.c
@@ -1401,16 +1401,23 @@ static int sh_eth_rx(struct net_device *ndev, u32 intr_status)
                 desc_status = edmac_to_cpu(mdp, rxdesc->status);
                 pkt_len = rxdesc->frame_length;
 
-#if defined(CONFIG_ARCH_R8A7740)
-                desc_status >>= 16;
-#endif
-
                 if (--boguscnt < 0)
                         break;
 
                 if (!(desc_status & RDFEND))
                         ndev->stats.rx_length_errors++;
 
+#if defined(CONFIG_ARCH_R8A7740)
+                /*
+                 * In case of almost all GETHER/ETHERs, the Receive Frame State
+                 * (RFS) bits in the Receive Descriptor 0 are from bit 9 to
+                 * bit 0. However, in case of the R8A7740's GETHER, the RFS
+                 * bits are from bit 25 to bit 16. So, the driver needs right
+                 * shifting by 16.
+                 */
+                desc_status >>= 16;
+#endif
+
                 if (desc_status & (RD_RFS1 | RD_RFS2 | RD_RFS3 | RD_RFS4 |
                                    RD_RFS5 | RD_RFS6 | RD_RFS10)) {
                         ndev->stats.rx_errors++;