[PATCH net-next 1/4] tsnep: Throttle interrupts

[Gerhard Engleder <gerhard@engleder-embedded.com>]

Without interrupt throttling, iperf server mode generates a CPU load of
100% (A53 1.2GHz). Also the throughput suffers with less than 900Mbit/s
on a 1Gbit/s link. The reason is a high interrupt load with interrupts
every ~20us.

Reduce interrupt load by throttling of interrupts. Interrupt delay is
configured statically to 64us. For iperf server mode the CPU load is
significantly reduced to ~20% and the throughput reaches the maximum of
941MBit/s. Interrupts are generated every ~140us.

Signed-off-by: Gerhard Engleder <gerhard@engleder-embedded.com>
---
 drivers/net/ethernet/engleder/tsnep_hw.h   | 7 +++++++
 drivers/net/ethernet/engleder/tsnep_main.c | 6 ++++++
 2 files changed, 13 insertions(+)

diff --git a/drivers/net/ethernet/engleder/tsnep_hw.h b/drivers/net/ethernet/engleder/tsnep_hw.h
index 315dada75323..55e1caf193a6 100644
--- a/drivers/net/ethernet/engleder/tsnep_hw.h
+++ b/drivers/net/ethernet/engleder/tsnep_hw.h
@@ -48,6 +48,13 @@
 #define ECM_COUNTER_LOW 0x0028
 #define ECM_COUNTER_HIGH 0x002C
 
+/* interrupt delay */
+#define ECM_INT_DELAY 0x0030
+#define ECM_INT_DELAY_MASK 0xF0
+#define ECM_INT_DELAY_SHIFT 4
+#define ECM_INT_DELAY_BASE_US 16
+#define ECM_INT_DELAY_OFFSET 1
+
 /* control and status */
 #define ECM_STATUS 0x0080
 #define ECM_LINK_MODE_OFF 0x01000000
diff --git a/drivers/net/ethernet/engleder/tsnep_main.c b/drivers/net/ethernet/engleder/tsnep_main.c
index 48fb391951dd..a99320e03279 100644
--- a/drivers/net/ethernet/engleder/tsnep_main.c
+++ b/drivers/net/ethernet/engleder/tsnep_main.c
@@ -39,6 +39,8 @@
 #endif
 #define DMA_ADDR_LOW(dma_addr) ((u32)((dma_addr) & 0xFFFFFFFF))
 
+#define INT_DELAY (64 / ECM_INT_DELAY_BASE_US)
+
 static void tsnep_enable_irq(struct tsnep_adapter *adapter, u32 mask)
 {
 	iowrite32(mask, adapter->addr + ECM_INT_ENABLE);
@@ -1298,6 +1300,7 @@ static int tsnep_phy_init(struct tsnep_adapter *adapter)
 static int tsnep_queue_init(struct tsnep_adapter *adapter, int queue_count)
 {
 	u32 irq_mask = ECM_INT_TX_0 | ECM_INT_RX_0;
+	u8 irq_delay = (INT_DELAY << ECM_INT_DELAY_SHIFT) & ECM_INT_DELAY_MASK;
 	char name[8];
 	int i;
 	int retval;
@@ -1316,6 +1319,7 @@ static int tsnep_queue_init(struct tsnep_adapter *adapter, int queue_count)
 	adapter->queue[0].tx = &adapter->tx[0];
 	adapter->queue[0].rx = &adapter->rx[0];
 	adapter->queue[0].irq_mask = irq_mask;
+	iowrite8(irq_delay, adapter->addr + ECM_INT_DELAY);
 
 	adapter->netdev->irq = adapter->queue[0].irq;
 
@@ -1336,6 +1340,8 @@ static int tsnep_queue_init(struct tsnep_adapter *adapter, int queue_count)
 		adapter->queue[i].rx = &adapter->rx[i];
 		adapter->queue[i].irq_mask =
 			irq_mask << (ECM_INT_TXRX_SHIFT * i);
+		iowrite8(irq_delay, adapter->addr + ECM_INT_DELAY +
+				    ECM_INT_DELAY_OFFSET * i);
 	}
 
 	return 0;
-- 
2.30.2