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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 19 insertions, 8 deletions

diff --git a/drivers/net/usb/dm9601.c b/drivers/net/usb/dm9601.c
index 732a926e3f51..c0bfc818c701 100644
--- a/drivers/net/usb/dm9601.c
+++ b/drivers/net/usb/dm9601.c
@@ -473,7 +473,7 @@ 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
@@ -481,12 +481,23 @@ 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)
@@ -495,10 +506,10 @@ 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;