net: ena: Remove CQ tail pointer update

The functionality was added to allow the drivers to create an
SQ and CQ of different sizes.
When the RX/TX SQ and CQ have the same size, such update isn't
necessary as the device can safely assume it doesn't override
unprocessed completions. However, if the SQ is larger than the CQ,
the device might "have" more completions it wants to update about
than there's room in the CQ.

There's no support for different SQ and CQ sizes, therefore,
removing the API and its usage.

'____cacheline_aligned' compiler attribute was added to
'struct ena_com_io_cq' to ensure that the removal of the
'cq_head_db_reg' field doesn't change the cache-line layout
of this struct.
Signed-off-by: Shay Agroskin <shayagr@amazon.com>
Signed-off-by: David Arinzon <darinzon@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/ethernet/amazon/ena/ena_com.c

@@ -1427,11 +1427,6 @@ int ena_com_create_io_cq(struct ena_com_dev *ena_dev,
 	io_cq->unmask_reg = (u32 __iomem *)((uintptr_t)ena_dev->reg_bar +
 		cmd_completion.cq_interrupt_unmask_register_offset);
 
-	if (cmd_completion.cq_head_db_register_offset)
-		io_cq->cq_head_db_reg =
-			(u32 __iomem *)((uintptr_t)ena_dev->reg_bar +
-			cmd_completion.cq_head_db_register_offset);
-
 	if (cmd_completion.numa_node_register_offset)
 		io_cq->numa_node_cfg_reg =
 			(u32 __iomem *)((uintptr_t)ena_dev->reg_bar +

drivers/net/ethernet/amazon/ena/ena_com.h

@@ -109,16 +109,13 @@ struct ena_com_io_cq {
 	/* Interrupt unmask register */
 	u32 __iomem *unmask_reg;
 
-	/* The completion queue head doorbell register */
-	u32 __iomem *cq_head_db_reg;
-
 	/* numa configuration register (for TPH) */
 	u32 __iomem *numa_node_cfg_reg;
 
 	/* The value to write to the above register to unmask
 	 * the interrupt of this queue
 	 */
-	u32 msix_vector;
+	u32 msix_vector ____cacheline_aligned;
 
 	enum queue_direction direction;
 
@@ -134,7 +131,6 @@ struct ena_com_io_cq {
 	/* Device queue index */
 	u16 idx;
 	u16 head;
-	u16 last_head_update;
 	u8 phase;
 	u8 cdesc_entry_size_in_bytes;
 

drivers/net/ethernet/amazon/ena/ena_eth_com.h

@@ -8,8 +8,6 @@
 
 #include "ena_com.h"
 
-/* head update threshold in units of (queue size / ENA_COMP_HEAD_THRESH) */
-#define ENA_COMP_HEAD_THRESH 4
 /* we allow 2 DMA descriptors per LLQ entry */
 #define ENA_LLQ_ENTRY_DESC_CHUNK_SIZE	(2 * sizeof(struct ena_eth_io_tx_desc))
 #define ENA_LLQ_HEADER		(128UL - ENA_LLQ_ENTRY_DESC_CHUNK_SIZE)
@@ -172,28 +170,6 @@ static inline int ena_com_write_sq_doorbell(struct ena_com_io_sq *io_sq)
 	return 0;
 }
 
-static inline int ena_com_update_dev_comp_head(struct ena_com_io_cq *io_cq)
-{
-	u16 unreported_comp, head;
-	bool need_update;
-
-	if (unlikely(io_cq->cq_head_db_reg)) {
-		head = io_cq->head;
-		unreported_comp = head - io_cq->last_head_update;
-		need_update = unreported_comp > (io_cq->q_depth / ENA_COMP_HEAD_THRESH);
-
-		if (unlikely(need_update)) {
-			netdev_dbg(ena_com_io_cq_to_ena_dev(io_cq)->net_device,
-				   "Write completion queue doorbell for queue %d: head: %d\n",
-				   io_cq->qid, head);
-			writel(head, io_cq->cq_head_db_reg);
-			io_cq->last_head_update = head;
-		}
-	}
-
-	return 0;
-}
-
 static inline void ena_com_update_numa_node(struct ena_com_io_cq *io_cq,
 					    u8 numa_node)
 {

drivers/net/ethernet/amazon/ena/ena_netdev.c

@@ -856,7 +856,6 @@ static int ena_clean_tx_irq(struct ena_ring *tx_ring, u32 budget)
 
 	tx_ring->next_to_clean = next_to_clean;
 	ena_com_comp_ack(tx_ring->ena_com_io_sq, total_done);
-	ena_com_update_dev_comp_head(tx_ring->ena_com_io_cq);
 
 	netdev_tx_completed_queue(txq, tx_pkts, tx_bytes);
 
@@ -1303,10 +1302,8 @@ static int ena_clean_rx_irq(struct ena_ring *rx_ring, struct napi_struct *napi,
 		      ENA_RX_REFILL_THRESH_PACKET);
 
 	/* Optimization, try to batch new rx buffers */
-	if (refill_required > refill_threshold) {
-		ena_com_update_dev_comp_head(rx_ring->ena_com_io_cq);
+	if (refill_required > refill_threshold)
 		ena_refill_rx_bufs(rx_ring, refill_required);
-	}
 
 	if (xdp_flags & ENA_XDP_REDIRECT)
 		xdp_do_flush();

drivers/net/ethernet/amazon/ena/ena_xdp.c

@@ -412,7 +412,6 @@ static int ena_clean_xdp_irq(struct ena_ring *tx_ring, u32 budget)
 
 	tx_ring->next_to_clean = next_to_clean;
 	ena_com_comp_ack(tx_ring->ena_com_io_sq, total_done);
-	ena_com_update_dev_comp_head(tx_ring->ena_com_io_cq);
 
 	netif_dbg(tx_ring->adapter, tx_done, tx_ring->netdev,
 		  "tx_poll: q %d done. total pkts: %d\n",