sfc: Fix efx_rx_buf_offset() in the presence of swiotlb

[ Upstream commits 06e63c57,
  b590ace0 and
  c73e787a ]

We assume that the mapping between DMA and virtual addresses is done
on whole pages, so we can find the page offset of an RX buffer using
the lower bits of the DMA address.  However, swiotlb maps in units of
2K, breaking this assumption.

Add an explicit page_offset field to struct efx_rx_buffer.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/net/ethernet/sfc/net_driver.h

@@ -213,6 +213,7 @@ struct efx_tx_queue {
  *	If both this and page are %NULL, the buffer slot is currently free.
  * @page: The associated page buffer, if any.
  *	If both this and skb are %NULL, the buffer slot is currently free.
+ * @page_offset: Offset within page. Valid iff @flags & %EFX_RX_BUF_PAGE.
  * @len: Buffer length, in bytes.
  * @is_page: Indicates if @page is valid. If false, @skb is valid.
  */
@@ -222,7 +223,8 @@ struct efx_rx_buffer {
 		struct sk_buff *skb;
 		struct page *page;
 	} u;
-	unsigned int len;
+	u16 page_offset;
+	u16 len;
 	bool is_page;
 };
 

drivers/net/ethernet/sfc/rx.c

@@ -95,11 +95,7 @@ static unsigned int rx_refill_limit = 95;
 static inline unsigned int efx_rx_buf_offset(struct efx_nic *efx,
 					     struct efx_rx_buffer *buf)
 {
-	/* Offset is always within one page, so we don't need to consider
-	 * the page order.
-	 */
-	return (((__force unsigned long) buf->dma_addr & (PAGE_SIZE - 1)) +
-		efx->type->rx_buffer_hash_size);
+	return buf->page_offset + efx->type->rx_buffer_hash_size;
 }
 static inline unsigned int efx_rx_buf_size(struct efx_nic *efx)
 {
@@ -194,6 +190,7 @@ static int efx_init_rx_buffers_page(struct efx_rx_queue *rx_queue)
 	struct efx_rx_buffer *rx_buf;
 	struct page *page;
 	void *page_addr;
+	unsigned int page_offset;
 	struct efx_rx_page_state *state;
 	dma_addr_t dma_addr;
 	unsigned index, count;
@@ -220,12 +217,14 @@ static int efx_init_rx_buffers_page(struct efx_rx_queue *rx_queue)
 
 		page_addr += sizeof(struct efx_rx_page_state);
 		dma_addr += sizeof(struct efx_rx_page_state);
+		page_offset = sizeof(struct efx_rx_page_state);
 
 	split:
 		index = rx_queue->added_count & rx_queue->ptr_mask;
 		rx_buf = efx_rx_buffer(rx_queue, index);
 		rx_buf->dma_addr = dma_addr + EFX_PAGE_IP_ALIGN;
 		rx_buf->u.page = page;
+		rx_buf->page_offset = page_offset + EFX_PAGE_IP_ALIGN;
 		rx_buf->len = efx->rx_buffer_len - EFX_PAGE_IP_ALIGN;
 		rx_buf->is_page = true;
 		++rx_queue->added_count;
@@ -237,6 +236,7 @@ static int efx_init_rx_buffers_page(struct efx_rx_queue *rx_queue)
 			get_page(page);
 			dma_addr += (PAGE_SIZE >> 1);
 			page_addr += (PAGE_SIZE >> 1);
+			page_offset += (PAGE_SIZE >> 1);
 			++count;
 			goto split;
 		}