diff options
Diffstat (limited to 'drivers/net/lib8390.c')
| -rw-r--r-- | drivers/net/lib8390.c | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/drivers/net/lib8390.c b/drivers/net/lib8390.c index 721ee38d2241..c429a5002dd6 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] */ |