bgmac: fix DMA rx corruption

The driver needs to inform the hardware about the first invalid (not yet
filled) rx slot, by writing its DMA descriptor pointer offset to the
BGMAC_DMA_RX_INDEX register.

This register was set to a value exceeding the rx ring size, effectively
allowing the hardware constant access to the full ring, regardless of
which slots are initialized.

To fix this issue, always mark the last filled rx slot as invalid.

Signed-off-by: Felix Fietkau <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/broadcom/bgmac.c

···
 	return 0;
 }
 
+static void bgmac_dma_rx_update_index(struct bgmac *bgmac,
+				      struct bgmac_dma_ring *ring)
+{
+	dma_wmb();
+
+	bgmac_write(bgmac, ring->mmio_base + BGMAC_DMA_RX_INDEX,
+		    ring->index_base +
+		    ring->end * sizeof(struct bgmac_dma_desc));
+}
+
 static void bgmac_dma_rx_setup_desc(struct bgmac *bgmac,
 				    struct bgmac_dma_ring *ring, int desc_idx)
 {
···
 	dma_desc->addr_high = cpu_to_le32(upper_32_bits(ring->slots[desc_idx].dma_addr));
 	dma_desc->ctl0 = cpu_to_le32(ctl0);
 	dma_desc->ctl1 = cpu_to_le32(ctl1);
+
+	ring->end = desc_idx;
 }
 
 static void bgmac_dma_rx_poison_buf(struct device *dma_dev,
···
 	end_slot &= BGMAC_DMA_RX_STATDPTR;
 	end_slot /= sizeof(struct bgmac_dma_desc);
 
-	ring->end = end_slot;
-
-	while (ring->start != ring->end) {
+	while (ring->start != end_slot) {
 		struct device *dma_dev = bgmac->core->dma_dev;
 		struct bgmac_slot_info *slot = &ring->slots[ring->start];
 		struct bgmac_rx_header *rx = slot->buf + BGMAC_RX_BUF_OFFSET;
···
 		if (handled >= weight) /* Should never be greater */
 			break;
 	}
+
+	bgmac_dma_rx_update_index(bgmac, ring);
 
 	return handled;
 }
···
 		if (ring->unaligned)
 			bgmac_dma_rx_enable(bgmac, ring);
 
+		ring->start = 0;
+		ring->end = 0;
 		for (j = 0; j < ring->num_slots; j++) {
 			err = bgmac_dma_rx_skb_for_slot(bgmac, &ring->slots[j]);
 			if (err)
···
 			bgmac_dma_rx_setup_desc(bgmac, ring, j);
 		}
 
-		bgmac_write(bgmac, ring->mmio_base + BGMAC_DMA_RX_INDEX,
-			    ring->index_base +
-			    ring->num_slots * sizeof(struct bgmac_dma_desc));
-
-		ring->start = 0;
-		ring->end = 0;
+		bgmac_dma_rx_update_index(bgmac, ring);
 	}
 
 	return 0;