Merge branch 'upstream-linus' of master.kernel.org:/pub/scm/linux/kernel/git/jgarzik/netdev-2.6

* 'upstream-linus' of master.kernel.org:/pub/scm/linux/kernel/git/jgarzik/netdev-2.6:
  Fix a potential NULL pointer dereference in mace_interrupt() in drivers/net/pcmcia/nmclan_cs.c
  PATCH kernel 2.6.22] PCMCIA-NETDEV : modify smc91c92_cs.c to become SMP safe
  S2io: Increment received packet count correctly
  S2io: Fix crash when resetting adapter
  S2io: Mask spurious interrupts
  S2IO: Implementing review comments from old patches
  S2IO: Checking for the return value of pci map function
  S2IO: Removing MSI support from driver
  S2IO: Removing 3 buffer mode support from the driver
  netxen: drop redudant spinlock
  netxen: Fix interrupt handling for multiport adapters
  netxen: re-init station address after h/w init
  tulip: Remove tulip maintainer
  forcedeth: mac address correct
  gfar: Fix modpost warning
  lib8390: comment on locking by Alan Cox
  Fix a potential NULL pointer dereference in write_bulk_callback() in drivers/net/usb/pegasus.c

1 files changed, 46 insertions, 0 deletions

diff --git a/drivers/net/lib8390.c b/drivers/net/lib8390.c
index 721ee38d224..c429a5002dd 100644
--- a/drivers/net/lib8390.c
+++ b/drivers/net/lib8390.c
@@ -143,6 +143,52 @@ static void __NS8390_init(struct net_device *dev, int startp);
  *	annoying the transmit function is called bh atomic. That places
  *	restrictions on the user context callers as disable_irq won't save
  *	them.
+ *
+ *	Additional explanation of problems with locking by Alan Cox:
+ *
+ *	"The author (me) didn't use spin_lock_irqsave because the slowness of the
+ *	card means that approach caused horrible problems like losing serial data
+ *	at 38400 baud on some chips. Rememeber many 8390 nics on PCI were ISA
+ *	chips with FPGA front ends.
+ *	
+ *	Ok the logic behind the 8390 is very simple:
+ *	
+ *	Things to know
+ *		- IRQ delivery is asynchronous to the PCI bus
+ *		- Blocking the local CPU IRQ via spin locks was too slow
+ *		- The chip has register windows needing locking work
+ *	
+ *	So the path was once (I say once as people appear to have changed it
+ *	in the mean time and it now looks rather bogus if the changes to use
+ *	disable_irq_nosync_irqsave are disabling the local IRQ)
+ *	
+ *	
+ *		Take the page lock
+ *		Mask the IRQ on chip
+ *		Disable the IRQ (but not mask locally- someone seems to have
+ *			broken this with the lock validator stuff)
+ *			[This must be _nosync as the page lock may otherwise
+ *				deadlock us]
+ *		Drop the page lock and turn IRQs back on
+ *		
+ *		At this point an existing IRQ may still be running but we can't
+ *		get a new one
+ *	
+ *		Take the lock (so we know the IRQ has terminated) but don't mask
+ *	the IRQs on the processor
+ *		Set irqlock [for debug]
+ *	
+ *		Transmit (slow as ****)
+ *	
+ *		re-enable the IRQ
+ *	
+ *	
+ *	We have to use disable_irq because otherwise you will get delayed
+ *	interrupts on the APIC bus deadlocking the transmit path.
+ *	
+ *	Quite hairy but the chip simply wasn't designed for SMP and you can't
+ *	even ACK an interrupt without risking corrupting other parallel
+ *	activities on the chip." [lkml, 25 Jul 2007]
  */