dm9601: work around tx fifo sync issue on dm962x

commit 4263c86dca5198da6bd3ad826d0b2304fbe25776 upstream.

Certain dm962x revisions contain an bug, where if a USB bulk transfer retry
(E.G. if bulk crc mismatch) happens right after a transfer with odd or
maxpacket length, the internal tx hardware fifo gets out of sync causing
the interface to stop working.

Work around it by adding up to 3 bytes of padding to ensure this situation
cannot trigger.

This workaround also means we never pass multiple-of-maxpacket size skb's
to usbnet, so the length adjustment to handle usbnet's padding of those can
be removed.

Reported-by: Joseph Chang <joseph_chang@davicom.com.tw>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/net/usb/dm9601.c b/drivers/net/usb/dm9601.c
index aaf7962..dc60aec 100644 (file)
--- a/drivers/net/usb/dm9601.c
+++ b/drivers/net/usb/dm9601.c
@@ -536,7 +536,7 @@ static int dm9601_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 static struct sk_buff *dm9601_tx_fixup(struct usbnet *dev, struct sk_buff *skb,
                                       gfp_t flags)
 {
-       int len;
+       int len, pad;
 
        /* format:
           b1: packet length low
@@ -544,12 +544,23 @@ static struct sk_buff *dm9601_tx_fixup(struct usbnet *dev, struct sk_buff *skb,
           b3..n: packet data
        */
 
-       len = skb->len;
+       len = skb->len + DM_TX_OVERHEAD;
+
+       /* workaround for dm962x errata with tx fifo getting out of
+        * sync if a USB bulk transfer retry happens right after a
+        * packet with odd / maxpacket length by adding up to 3 bytes
+        * padding.
+        */
+       while ((len & 1) || !(len % dev->maxpacket))
+               len++;
 
-       if (skb_headroom(skb) < DM_TX_OVERHEAD) {
+       len -= DM_TX_OVERHEAD; /* hw header doesn't count as part of length */
+       pad = len - skb->len;
+
+       if (skb_headroom(skb) < DM_TX_OVERHEAD || skb_tailroom(skb) < pad) {
                struct sk_buff *skb2;
 
-               skb2 = skb_copy_expand(skb, DM_TX_OVERHEAD, 0, flags);
+               skb2 = skb_copy_expand(skb, DM_TX_OVERHEAD, pad, flags);
                dev_kfree_skb_any(skb);
                skb = skb2;
                if (!skb)
@@ -558,10 +569,10 @@ static struct sk_buff *dm9601_tx_fixup(struct usbnet *dev, struct sk_buff *skb,
 
        __skb_push(skb, DM_TX_OVERHEAD);
 
-       /* usbnet adds padding if length is a multiple of packet size
-          if so, adjust length value in header */
-       if ((skb->len % dev->maxpacket) == 0)
-               len++;
+       if (pad) {
+               memset(skb->data + skb->len, 0, pad);
+               __skb_put(skb, pad);
+       }
 
        skb->data[0] = len;
        skb->data[1] = len >> 8;