sfc: Replace some literal constants with EFX_PAGE_SIZE/EFX_BUF_SIZE

The 'page size' for PCIe DMA, i.e. the alignment of boundaries at
which DMA must be broken, is 4KB.  Name this value as EFX_PAGE_SIZE
and use it in efx_max_tx_len().  Redefine EFX_BUF_SIZE as
EFX_PAGE_SIZE since its value is also a result of that requirement,
and use it in efx_init_special_buffer().
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

drivers/net/ethernet/sfc/nic.c

@@ -54,9 +54,6 @@
 #define EFX_FLUSH_INTERVAL 10
 #define EFX_FLUSH_POLL_COUNT 100
 
-/* Size and alignment of special buffers (4KB) */
-#define EFX_BUF_SIZE 4096
-
 /* Depth of RX flush request fifo */
 #define EFX_RX_FLUSH_COUNT 4
 
@@ -196,7 +193,7 @@ efx_init_special_buffer(struct efx_nic *efx, struct efx_special_buffer *buffer)
 	/* Write buffer descriptors to NIC */
 	for (i = 0; i < buffer->entries; i++) {
 		index = buffer->index + i;
-		dma_addr = buffer->dma_addr + (i * 4096);
+		dma_addr = buffer->dma_addr + (i * EFX_BUF_SIZE);
 		netif_dbg(efx, probe, efx->net_dev,
 			  "mapping special buffer %d at %llx\n",
 			  index, (unsigned long long)dma_addr);

drivers/net/ethernet/sfc/nic.h

@@ -65,6 +65,11 @@ enum {
 #define FALCON_GMAC_LOOPBACKS			\
 	(1 << LOOPBACK_GMAC)
 
+/* Alignment of PCIe DMA boundaries (4KB) */
+#define EFX_PAGE_SIZE	4096
+/* Size and alignment of buffer table entries (same) */
+#define EFX_BUF_SIZE	EFX_PAGE_SIZE
+
 /**
  * struct falcon_board_type - board operations and type information
  * @id: Board type id, as found in NVRAM

drivers/net/ethernet/sfc/tx.c

@@ -110,7 +110,7 @@ efx_max_tx_len(struct efx_nic *efx, dma_addr_t dma_addr)
 	 * little benefit from using descriptors that cross those
 	 * boundaries and we keep things simple by not doing so.
 	 */
-	unsigned len = (~dma_addr & 0xfff) + 1;
+	unsigned len = (~dma_addr & (EFX_PAGE_SIZE - 1)) + 1;
 
 	/* Work around hardware bug for unaligned buffers. */
 	if (EFX_WORKAROUND_5391(efx) && (dma_addr & 0xf))