[PATCH net] net: bgmac: fix TX DMA unmapping on fragment mapping failure

[Rosen Penev <rosenp@gmail.com>]

When mapping a fragment fails, bgmac_dma_tx_add() unwinds with the
wrong slots. It passes the failed fragment's slot->dma_addr, which
holds the mapping error, to dma_unmap_single() for the head. The
fragment loop indexes from ring->end instead of ring->end + 1, so it
unmaps the head a second time as a page and leaves the last mapped
fragment mapped.

None of the affected slots get their dma_addr cleared either, which
includes the head slot when mapping the head fails.
bgmac_dma_tx_ring_free() unmaps every slot with a non-zero dma_addr,
so tearing down the ring unmaps these addresses again.

Unmap the head and each mapped fragment from their own slots, and
clear dma_addr on every slot the failed packet touched.

Fixes: 9cde94506eac ("bgmac: implement scatter/gather support")
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/net/ethernet/broadcom/bgmac.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bgmac.c b/drivers/net/ethernet/broadcom/bgmac.c
index 1835266fdd09..134eff89f787 100644
--- a/drivers/net/ethernet/broadcom/bgmac.c
+++ b/drivers/net/ethernet/broadcom/bgmac.c
@@ -208,19 +208,24 @@ static netdev_tx_t bgmac_dma_tx_add(struct bgmac *bgmac,
 	return NETDEV_TX_OK;
 
 err_dma:
-	dma_unmap_single(dma_dev, slot->dma_addr, skb_headlen(skb),
-			 DMA_TO_DEVICE);
+	slot->dma_addr = 0;
 
 	while (i-- > 0) {
-		int index = (ring->end + i) % BGMAC_TX_RING_SLOTS;
-		struct bgmac_slot_info *slot = &ring->slots[index];
-		u32 ctl1 = le32_to_cpu(ring->cpu_base[index].ctl1);
-		int len = ctl1 & BGMAC_DESC_CTL1_LEN;
-
-		dma_unmap_page(dma_dev, slot->dma_addr, len, DMA_TO_DEVICE);
+		index = (ring->end + 1 + i) % BGMAC_TX_RING_SLOTS;
+		slot = &ring->slots[index];
+		dma_unmap_page(dma_dev, slot->dma_addr,
+			       skb_frag_size(&skb_shinfo(skb)->frags[i]),
+			       DMA_TO_DEVICE);
+		slot->dma_addr = 0;
 	}
 
+	slot = &ring->slots[ring->end % BGMAC_TX_RING_SLOTS];
+	dma_unmap_single(dma_dev, slot->dma_addr, skb_headlen(skb),
+			 DMA_TO_DEVICE);
+
 err_dma_head:
+	slot->dma_addr = 0;
+
 	netdev_err(bgmac->net_dev, "Mapping error of skb on ring 0x%X\n",
 		   ring->mmio_base);
 
-- 
2.56.0