[ Upstream commit 536d3680fd2dab5c39857d62a3e084198fc74ff9 ]
The ks8851 driver lets the chip auto-dequeue received packets once they have been read in full. It achieves that by setting the ADRFE flag in the RXQCR register ("Auto-Dequeue RXQ Frame Enable").
However if allocation of a packet's socket buffer or retrieval of the packet over the SPI bus fails, the packet will not have been read in full and is not auto-dequeued. Such partial retrieval of a packet confuses the chip's RX queue management: On the next RX interrupt, the first packet read from the queue will be the one left there previously and this one can be retrieved without issues. But for any newly received packets, the frame header status and byte count registers (RXFHSR and RXFHBCR) contain bogus values, preventing their retrieval.
The chip allows explicitly dequeueing a packet from the RX queue by setting the RRXEF flag in the RXQCR register ("Release RX Error Frame"). This could be used to dequeue the packet in case of an error, but if that error is a failed SPI transfer, it is unknown if the packet was transferred in full and was auto-dequeued or if it was only transferred in part and requires an explicit dequeue. The safest approach is thus to always dequeue packets explicitly and forgo auto-dequeueing.
Without this change, I've witnessed packet retrieval break completely when an SPI DMA transfer fails, requiring a chip reset. Explicit dequeueing magically fixes this and makes packet retrieval absolutely robust for me.
The chip's documentation suggests auto-dequeuing and uses the RRXEF flag only to dequeue error frames which the driver doesn't want to retrieve. But that seems to be a fair-weather approach.
Signed-off-by: Lukas Wunner lukas@wunner.de Cc: Frank Pavlic f.pavlic@kunbus.de Cc: Ben Dooks ben.dooks@codethink.co.uk Cc: Tristram Ha Tristram.Ha@microchip.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin (Microsoft) sashal@kernel.org --- drivers/net/ethernet/micrel/ks8851.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/net/ethernet/micrel/ks8851.c b/drivers/net/ethernet/micrel/ks8851.c index 1edc973df4c4..247a3377b951 100644 --- a/drivers/net/ethernet/micrel/ks8851.c +++ b/drivers/net/ethernet/micrel/ks8851.c @@ -547,9 +547,8 @@ static void ks8851_rx_pkts(struct ks8851_net *ks) /* set dma read address */ ks8851_wrreg16(ks, KS_RXFDPR, RXFDPR_RXFPAI | 0x00);
- /* start the packet dma process, and set auto-dequeue rx */ - ks8851_wrreg16(ks, KS_RXQCR, - ks->rc_rxqcr | RXQCR_SDA | RXQCR_ADRFE); + /* start DMA access */ + ks8851_wrreg16(ks, KS_RXQCR, ks->rc_rxqcr | RXQCR_SDA);
if (rxlen > 4) { unsigned int rxalign; @@ -580,7 +579,8 @@ static void ks8851_rx_pkts(struct ks8851_net *ks) } }
- ks8851_wrreg16(ks, KS_RXQCR, ks->rc_rxqcr); + /* end DMA access and dequeue packet */ + ks8851_wrreg16(ks, KS_RXQCR, ks->rc_rxqcr | RXQCR_RRXEF); } }