From 963267bc5d4de4a0da104a64300375d186575332 Mon Sep 17 00:00:00 2001 From: "Maciej W. Rozycki" Date: Mon, 8 Jun 2009 02:42:35 -0700 Subject: [PATCH] declance: Restore tx descriptor ring locking A driver overhaul on 29 Feb 2000 (!) broke locking around fiddling with the tx descriptor ring in start_xmit(); a follow-on "fix" removed the broken remnants altogether. Here's a patch to restore proper locking in the function -- the complement in the interrupt handler has been correct all the time. This *may* have been the reason for the occasional confusion of the chip -- triggering a tx timeout followed by a chip reset sequence -- seen on R4k-based DECstations with the onboard Ethernet interface. Another theory is the confusion is due to an unindentified problem -- perhaps a silicon erratum -- associated with the variation of the MT ASIC used to interface the R4k CPU to the rest of the system on these computers; with its aggressive write-back buffering the design is particularly weakly ordered when it comes to MMIO (in the absence of ordering barriers uncached reads are allowed to bypass earlier uncached writes, even if to the same location), which may trigger all kinds of corner cases in peripheral hardware as well as software. Either way this piece of code is buggy. Signed-off-by: Maciej W. Rozycki Signed-off-by: David S. Miller --- drivers/net/declance.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/drivers/net/declance.c b/drivers/net/declance.c index b62405a69180..2b22e580c4de 100644 --- a/drivers/net/declance.c +++ b/drivers/net/declance.c @@ -895,6 +895,7 @@ static int lance_start_xmit(struct sk_buff *skb, struct net_device *dev) struct lance_private *lp = netdev_priv(dev); volatile struct lance_regs *ll = lp->ll; volatile u16 *ib = (volatile u16 *)dev->mem_start; + unsigned long flags; int entry, len; len = skb->len; @@ -907,6 +908,8 @@ static int lance_start_xmit(struct sk_buff *skb, struct net_device *dev) dev->stats.tx_bytes += len; + spin_lock_irqsave(&lp->lock, flags); + entry = lp->tx_new; *lib_ptr(ib, btx_ring[entry].length, lp->type) = (-len); *lib_ptr(ib, btx_ring[entry].misc, lp->type) = 0; @@ -925,6 +928,8 @@ static int lance_start_xmit(struct sk_buff *skb, struct net_device *dev) /* Kick the lance: transmit now */ writereg(&ll->rdp, LE_C0_INEA | LE_C0_TDMD); + spin_unlock_irqrestore(&lp->lock, flags); + dev->trans_start = jiffies; dev_kfree_skb(skb); -- 2.20.1