[net-next 3/3] ravb: TROCR register is only present on R-Car Gen3

[Simon Horman]

Only use the TROCR register on R-Car Gen3.
It is not present on other SoCs.

Offsets used for the undocumented registers are also considered reserved
and should not be written to.

After some internal investigation with Renesas it remains unclear why this
driver accesses these fields on R-Car Gen2 but regardless of what the
historical reasons are the current code is considered incorrect.

Signed-off-by: Simon Horman <horms+rene...@verge.net.au>
---
 drivers/net/ethernet/renesas/ravb.h      | 2 +-
 drivers/net/ethernet/renesas/ravb_main.c | 6 ++++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/renesas/ravb.h 
b/drivers/net/ethernet/renesas/ravb.h
index bdb051f04b0c..a9c89d5d8898 100644
--- a/drivers/net/ethernet/renesas/ravb.h
+++ b/drivers/net/ethernet/renesas/ravb.h
@@ -193,7 +193,7 @@ enum ravb_reg {
        GECMR   = 0x05b0,
        MAHR    = 0x05c0,
        MALR    = 0x05c8,
-       TROCR   = 0x0700,       /* Undocumented? */
+       TROCR   = 0x0700,       /* R-Car Gen3 only */
        CEFCR   = 0x0740,
        FRECR   = 0x0748,
        TSFRCR  = 0x0750,
diff --git a/drivers/net/ethernet/renesas/ravb_main.c 
b/drivers/net/ethernet/renesas/ravb_main.c
index b538cc6fdbb7..de9aa8c47f1c 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -1621,8 +1621,10 @@ static struct net_device_stats *ravb_get_stats(struct 
net_device *ndev)
        stats0 = &priv->stats[RAVB_BE];
        stats1 = &priv->stats[RAVB_NC];
 
-       nstats->tx_dropped += ravb_read(ndev, TROCR);
-       ravb_write(ndev, 0, TROCR);     /* (write clear) */
+       if (priv->chip_id == RCAR_GEN3) {
+               nstats->tx_dropped += ravb_read(ndev, TROCR);
+               ravb_write(ndev, 0, TROCR);     /* (write clear) */
+       }
 
        nstats->rx_packets = stats0->rx_packets + stats1->rx_packets;
        nstats->tx_packets = stats0->tx_packets + stats1->tx_packets;
-- 
2.11.0