Description of problem:

  Setting to anything <= 12 causes all network traffic to 'disappear',
  cannot ping, telnet, etc.
  Bringing the interface down, then setting to > 12 will correct the issue.


Version-Release number of selected component (if applicable):
  RHEL 5.3 x86_64 (-155 from dzickus tested as well)


How reproducible:
  Always


Relevant code:
static int bnx2x_set_coalesce(struct net_device *dev,
                             struct ethtool_coalesce *coal)
{
       struct bnx2x *bp = netdev_priv(dev);

       bp->rx_ticks = (u16) coal->rx_coalesce_usecs;
       if (bp->rx_ticks > 3000)
               bp->rx_ticks = 3000;
...
       if (netif_running(dev))
               bnx2x_update_coalesce(bp);

and

static void bnx2x_update_coalesce(struct bnx2x *bp)
{
               REG_WR8(bp, BAR_USTRORM_INTMEM +
                       USTORM_SB_HC_TIMEOUT_OFFSET(port, sb_id,
                                                   U_SB_ETH_RX_CQ_INDEX),
                       bp->rx_ticks/12);

Usually a code like that 'rx_ticks/12' means the board register accepts
multiples of 12, so you can configure 0us, 12us, 24us, 36us, 48us, 60us...
Upstream does that too.
Broadcom driver does that too.

I looks like a hardware limitation, though I don't have any detailed
board specification to make sure.

However, it should not stop working because someone tried to configure
a value less or equal 12us.