[PATCH net] net: bgmac: rate limit RX error messages

[Rosen Penev]

When the RX ring is full the RX FIFO overflows. With RX overflow
continue enabled, the DMA engine then writes one frame with a bogus
length (always 0x45c2 on a BCM4716), which the driver drops with
"Found oversized packet at slot %d, DMA issue!".

Under sustained overload this happens on every NAPI poll. On an Asus
RT-N16 a 950 Mbit/s UDP stream to the router printed about 1450 such
lines in 20 seconds. The messages are printed from NAPI context, so
with a serial console the router spends most of its time printing.

The frames are already accounted in rx_length_errors and rx_errors.
Rate limit both RX error messages. With this change the same flood
printed 60 lines while rx_length_errors counted 14297 dropped frames.

Fixes: 6a6c708469c9 ("bgmac: add check for oversized packets")
Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
---
 drivers/net/ethernet/broadcom/bgmac.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bgmac.c b/drivers/net/ethernet/broadcom/bgmac.c
index 1835266fdd09..b3a92ae95de3 100644
--- a/drivers/net/ethernet/broadcom/bgmac.c
+++ b/drivers/net/ethernet/broadcom/bgmac.c
@@ -447,16 +447,18 @@ static int bgmac_dma_rx_read(struct bgmac *bgmac, struct bgmac_dma_ring *ring,
 
 			/* Check for poison and drop or pass the packet */
 			if (len == 0xdead && flags == 0xbeef) {
-				netdev_err(bgmac->net_dev, "Found poisoned packet at slot %d, DMA issue!\n",
-					   ring->start);
+				if (net_ratelimit())
+					netdev_err(bgmac->net_dev, "Found poisoned packet at slot %d, DMA issue!\n",
+						   ring->start);
 				put_page(virt_to_head_page(buf));
 				bgmac->net_dev->stats.rx_errors++;
 				break;
 			}
 
 			if (len > BGMAC_RX_ALLOC_SIZE) {
-				netdev_err(bgmac->net_dev, "Found oversized packet at slot %d, DMA issue!\n",
-					   ring->start);
+				if (net_ratelimit())
+					netdev_err(bgmac->net_dev, "Found oversized packet at slot %d, DMA issue!\n",
+						   ring->start);
 				put_page(virt_to_head_page(buf));
 				bgmac->net_dev->stats.rx_length_errors++;
 				bgmac->net_dev->stats.rx_errors++;
-- 
2.56.0