sfc: Extend struct efx_tx_buffer to allow pushing option descriptors

The TX path firmware for EF10 supports 'option descriptors' to control
offloads and various other features.  Add a flag and field for these
in struct efx_tx_buffer, and don't treat them as DMA descriptors on
completion.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/farch.c

@@ -325,6 +325,8 @@ void efx_farch_tx_write(struct efx_tx_queue *tx_queue)
 		txd = efx_tx_desc(tx_queue, write_ptr);
 		++tx_queue->write_count;
 
+		EFX_BUG_ON_PARANOID(buffer->flags & EFX_TX_BUF_OPTION);
+
 		/* Create TX descriptor ring entry */
 		BUILD_BUG_ON(EFX_TX_BUF_CONT != 1);
 		EFX_POPULATE_QWORD_4(*txd,

drivers/net/ethernet/sfc/net_driver.h

@@ -135,6 +135,7 @@ struct efx_special_buffer {
  *	freed when descriptor completes
  * @heap_buf: When @flags & %EFX_TX_BUF_HEAP, the associated heap buffer to be
  *	freed when descriptor completes.
+ * @option: When @flags & %EFX_TX_BUF_OPTION, a NIC-specific option descriptor.
  * @dma_addr: DMA address of the fragment.
  * @flags: Flags for allocation and DMA mapping type
  * @len: Length of this fragment.
@@ -146,7 +147,10 @@ struct efx_tx_buffer {
 		const struct sk_buff *skb;
 		void *heap_buf;
 	};
-	dma_addr_t dma_addr;
+	union {
+		efx_qword_t option;
+		dma_addr_t dma_addr;
+	};
 	unsigned short flags;
 	unsigned short len;
 	unsigned short unmap_len;
@@ -155,6 +159,7 @@ struct efx_tx_buffer {
 #define EFX_TX_BUF_SKB		2	/* buffer is last part of skb */
 #define EFX_TX_BUF_HEAP		4	/* buffer was allocated with kmalloc() */
 #define EFX_TX_BUF_MAP_SINGLE	8	/* buffer was mapped with dma_map_single() */
+#define EFX_TX_BUF_OPTION	0x10	/* empty buffer for option descriptor */
 
 /**
  * struct efx_tx_queue - An Efx TX queue

drivers/net/ethernet/sfc/tx.c

@@ -306,7 +306,9 @@ static void efx_dequeue_buffers(struct efx_tx_queue *tx_queue,
 
 	while (read_ptr != stop_index) {
 		struct efx_tx_buffer *buffer = &tx_queue->buffer[read_ptr];
-		if (unlikely(buffer->len == 0)) {
+
+		if (!(buffer->flags & EFX_TX_BUF_OPTION) &&
+		    unlikely(buffer->len == 0)) {
 			netif_err(efx, tx_err, efx->net_dev,
 				  "TX queue %d spurious TX completion id %x\n",
 				  tx_queue->queue, read_ptr);