[PATCH] b43: use rx desc underrun interrupt

[Thommy Jakobsson]

Hi,

long user of b43 driver under openwrt. Not sure if it has been posted
previously but using slow and old hardware (as routers running openwrt
most of the time is), the CPU is sometimes slower than the NIC. So
recently I, and several others, has had problem of wifi going down.
See ticket 7552 at openwrt for more info
(https://dev.openwrt.org/ticket/7552)

I have tracked down the problem to the nic getting into a rx
descriptor underrun. Since the driver don't listen to that (or take
care of it in any other way), the Wifi seemingly just dies. The CPU is
waiting for data from the nic and the nic is waiting for a
confirmation that it can keep sending.

I created a patch for handling of that interrupt. I have tested it by
reducing the number of rx slots to 16 and sending a couple of 100GB of
data. Previously Wifi went down within a minute when maxing out the
uplink (so rx for AP), now it has been working flawless for a 1.5week.

BR,
Thommy Jakobsson

Index: drivers/net/wireless/b43/dma.c
===================================================================
--- compat-wireless-2012-09-07.orig/drivers/net/wireless/b43/dma.c
2013-04-09 17:33:54.325322046 +0200
+++ compat-wireless-2012-09-07/drivers/net/wireless/b43/dma.c
2013-04-09 17:34:43.473565843 +0200
@@ -1688,6 +1688,21 @@
         b43_poison_rx_buffer(ring, skb);
         sync_descbuffer_for_device(ring, dmaaddr, ring->rx_buffersize);
 }
+void b43_dma_rx_discard(struct b43_dmaring *ring)
+{
+   B43_WARN_ON(ring->tx);
+
+    /* Device has filled all buffers, drop all packets in buffers
+     * and let TCP decrease speed.
+     * Set index to one desc after the last one (which is marked)
+     * so the device will see all slots as free again
+     */
+    /*
+     *TODO: How to increase rx_drop in mac80211
+     */
+   b43_dma_write(ring, B43_DMA32_RXINDEX, ring->nr_slots *
+                                     sizeof(struct b43_dmadesc32));
+}

 void b43_dma_rx(struct b43_dmaring *ring)
 {

Index: drivers/net/wireless/b43/dma.h
===================================================================
--- compat-wireless-2012-09-07.orig/drivers/net/wireless/b43/dma.h
2013-04-09 17:34:09.561397686 +0200
+++ compat-wireless-2012-09-07/drivers/net/wireless/b43/dma.h
2013-04-09 17:34:43.461565780 +0200
@@ -10,7 +10,8 @@
 #define B43_DMAIRQ_FATALMASK    ((1 << 10) | (1 << 11) | (1 << 12) \
                                          | (1 << 14) | (1 << 15))
 #define B43_DMAIRQ_NONFATALMASK (1 << 13)
-#define B43_DMAIRQ_RX_DONE              (1 << 16)
+#define B43_DMAIRQ_RX_DONE      (1 << 16)
+#define B43_DMAIRQ_RDESC_UFLOW  (1 << 13)

 /*** 32-bit DMA Engine. ***/

@@ -295,6 +296,8 @@
 void b43_dma_handle_txstatus(struct b43_wldev *dev,
                              const struct b43_txstatus *status);

+void b43_dma_rx_discard(struct b43_dmaring *ring);
+
 void b43_dma_rx(struct b43_dmaring *ring);

 void b43_dma_direct_fifo_rx(struct b43_wldev *dev,

Index: drivers/net/wireless/b43/main.c
===================================================================
--- compat-wireless-2012-09-07.orig/drivers/net/wireless/b43/main.c
2013-04-09 17:33:54.325322046 +0200
+++ compat-wireless-2012-09-07/drivers/net/wireless/b43/main.c
2013-04-09 18:08:01.011471215 +0200
@@ -1894,14 +1894,6 @@
                         b43_controller_restart(dev, "DMA error");
                         return;
                 }
-                if (merged_dma_reason & B43_DMAIRQ_NONFATALMASK) {
-                        b43err(dev->wl, "DMA error: "
-                               "0x%08X, 0x%08X, 0x%08X, "
-                               "0x%08X, 0x%08X, 0x%08X\n",
-                               dma_reason[0], dma_reason[1],
-                               dma_reason[2], dma_reason[3],
-                               dma_reason[4], dma_reason[5]);
-                }
         }

         if (unlikely(reason & B43_IRQ_UCODE_DEBUG))
@@ -1920,6 +1912,14 @@
                 handle_irq_noise(dev);

         /* Check the DMA reason registers for received data. */
+        if (dma_reason[0] & B43_DMAIRQ_RDESC_UFLOW) {
+           //only print 256 time to not flood log
+           if(!(dev->stats.rxdesc_underruns++&0xFF)){
+                        b43warn(dev->wl, "Rx descriptor underrun
(high cpu load?), throwing packets\n");
+           }
+           b43_dma_rx_discard(dev->dma.rx_ring);
+
+        }
         if (dma_reason[0] & B43_DMAIRQ_RX_DONE) {
                 if (b43_using_pio_transfers(dev))
                         b43_pio_rx(dev->pio.rx_queue);
@@ -1977,7 +1977,7 @@
                 return IRQ_NONE;

         dev->dma_reason[0] = b43_read32(dev, B43_MMIO_DMA0_REASON)
-            & 0x0001DC00;
+            & 0x0001FC00;
         dev->dma_reason[1] = b43_read32(dev, B43_MMIO_DMA1_REASON)
             & 0x0000DC00;
         dev->dma_reason[2] = b43_read32(dev, B43_MMIO_DMA2_REASON)
@@ -3081,7 +3081,7 @@
                 b43_write32(dev, 0x018C, 0x02000000);
         }
         b43_write32(dev, B43_MMIO_GEN_IRQ_REASON, 0x00004000);
-        b43_write32(dev, B43_MMIO_DMA0_IRQ_MASK, 0x0001DC00);
+        b43_write32(dev, B43_MMIO_DMA0_IRQ_MASK, 0x0001FC00);
         b43_write32(dev, B43_MMIO_DMA1_IRQ_MASK, 0x0000DC00);
         b43_write32(dev, B43_MMIO_DMA2_IRQ_MASK, 0x0000DC00);
         b43_write32(dev, B43_MMIO_DMA3_IRQ_MASK, 0x0001DC00);

===================================================================
--- compat-wireless-2012-09-07.orig/drivers/net/wireless/b43/b43.h
2013-04-09 17:04:51.552680190 +0200
+++ compat-wireless-2012-09-07/drivers/net/wireless/b43/b43.h
2013-04-09 17:46:08.472962612 +0200
@@ -671,6 +671,7 @@

 struct b43_stats {
         u8 link_noise;
+        u32 rxdesc_underruns;
 };

 struct b43_key {