bgmac: simplify tx ring index handling

Keep incrementing ring->start and ring->end instead of pointing it to
the actual ring slot entry. This simplifies the calculation of the
number of free slots.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Acked-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 23 insertions, 29 deletions

diff --git a/drivers/net/ethernet/broadcom/bgmac.c b/drivers/net/ethernet/broadcom/bgmac.c
index fa8f9e147c34..b9e02e484d72 100644
--- a/drivers/net/ethernet/broadcom/bgmac.c
+++ b/drivers/net/ethernet/broadcom/bgmac.c
@@ -142,11 +142,10 @@ static netdev_tx_t bgmac_dma_tx_add(struct bgmac *bgmac,
 {
         struct device *dma_dev = bgmac->core->dma_dev;
         struct net_device *net_dev = bgmac->net_dev;
-        struct bgmac_slot_info *slot = &ring->slots[ring->end];
-        int free_slots;
+        int index = ring->end % BGMAC_TX_RING_SLOTS;
+        struct bgmac_slot_info *slot = &ring->slots[index];
         int nr_frags;
         u32 flags;
-        int index = ring->end;
         int i;
 
         if (skb->len > BGMAC_DESC_CTL1_LEN) {
@@ -159,12 +158,10 @@ static netdev_tx_t bgmac_dma_tx_add(struct bgmac *bgmac,
 
         nr_frags = skb_shinfo(skb)->nr_frags;
 
-        if (ring->start <= ring->end)
-                free_slots = ring->start - ring->end + BGMAC_TX_RING_SLOTS;
-        else
-                free_slots = ring->start - ring->end;
-
-        if (free_slots <= nr_frags + 1) {
+        /* ring->end - ring->start will return the number of valid slots,
+         * even when ring->end overflows
+         */
+        if (ring->end - ring->start + nr_frags + 1 >= BGMAC_TX_RING_SLOTS) {
                 bgmac_err(bgmac, "TX ring is full, queue should be stopped!\n");
                 netif_stop_queue(net_dev);
                 return NETDEV_TX_BUSY;
@@ -200,7 +197,7 @@ static netdev_tx_t bgmac_dma_tx_add(struct bgmac *bgmac,
         }
 
         slot->skb = skb;
-
+        ring->end += nr_frags + 1;
         netdev_sent_queue(net_dev, skb->len);
 
         wmb();
@@ -208,13 +205,12 @@ static netdev_tx_t bgmac_dma_tx_add(struct bgmac *bgmac,
         /* Increase ring->end to point empty slot. We tell hardware the first
          * slot it should *not* read.
          */
-        ring->end = (index + 1) % BGMAC_TX_RING_SLOTS;
         bgmac_write(bgmac, ring->mmio_base + BGMAC_DMA_TX_INDEX,
                     ring->index_base +
-                    ring->end * sizeof(struct bgmac_dma_desc));
+                    (ring->end % BGMAC_TX_RING_SLOTS) *
+                    sizeof(struct bgmac_dma_desc));
 
-        free_slots -= nr_frags + 1;
-        if (free_slots < 8)
+        if (ring->end - ring->start >= BGMAC_TX_RING_SLOTS - 8)
                 netif_stop_queue(net_dev);
 
         return NETDEV_TX_OK;
@@ -256,17 +252,17 @@ static void bgmac_dma_tx_free(struct bgmac *bgmac, struct bgmac_dma_ring *ring)
         empty_slot &= BGMAC_DMA_TX_STATDPTR;
         empty_slot /= sizeof(struct bgmac_dma_desc);
 
-        while (ring->start != empty_slot) {
-                struct bgmac_slot_info *slot = &ring->slots[ring->start];
-                u32 ctl1 = le32_to_cpu(ring->cpu_base[ring->start].ctl1);
-                int len = ctl1 & BGMAC_DESC_CTL1_LEN;
+        while (ring->start != ring->end) {
+                int slot_idx = ring->start % BGMAC_TX_RING_SLOTS;
+                struct bgmac_slot_info *slot = &ring->slots[slot_idx];
+                u32 ctl1;
+                int len;
 
-                if (!slot->dma_addr) {
-                        bgmac_err(bgmac, "Hardware reported transmission for empty TX ring slot %d! End of ring: %d\n",
-                                  ring->start, ring->end);
-                        goto next;
-                }
+                if (slot_idx == empty_slot)
+                        break;
 
+                ctl1 = le32_to_cpu(ring->cpu_base[slot_idx].ctl1);
+                len = ctl1 & BGMAC_DESC_CTL1_LEN;
                 if (ctl1 & BGMAC_DESC_CTL0_SOF)
                         /* Unmap no longer used buffer */
                         dma_unmap_single(dma_dev, slot->dma_addr, len,
@@ -284,10 +280,8 @@ static void bgmac_dma_tx_free(struct bgmac *bgmac, struct bgmac_dma_ring *ring)
                         slot->skb = NULL;
                 }
 
-next:
                 slot->dma_addr = 0;
-                if (++ring->start >= BGMAC_TX_RING_SLOTS)
-                        ring->start = 0;
+                ring->start++;
                 freed = true;
         }
 
diff --git a/drivers/net/ethernet/broadcom/bgmac.h b/drivers/net/ethernet/broadcom/bgmac.h
index 3ad965fe7fcc..5a198d56f3e7 100644
--- a/drivers/net/ethernet/broadcom/bgmac.h
+++ b/drivers/net/ethernet/broadcom/bgmac.h
@@ -414,10 +414,10 @@ enum bgmac_dma_ring_type {
  * empty.
  */
 struct bgmac_dma_ring {
-        u16 num_slots;
-        u16 start;
-        u16 end;
+        u32 start;
+        u32 end;
 
+        u16 num_slots;
         u16 mmio_base;
         struct bgmac_dma_desc *cpu_base;
         dma_addr_t dma_base;