cvs commit: src/sys/dev/fxp if_fxp.c if_fxpvar.h

[Justin T. Gibbs]

> : All doable things for all but really broken hardware.  fxp is not broken.
> 
> The whole reason for the gone flag may be misunderstood here.  You can
> easily turn off the fxp device, and there will be no more interrupts
> from it.  However, its ISR can and will still be called from time to
> time until the bus_teardown_intr() is complete?  Why you ask?

No, I didn't ask.  The same applies to *any* driver that can share interrupts.
This includes ahc and ahd.  I just assumed that the interrupt handler could
determine that the interrupt was not for it regardless of whether or not the
card is generating interrupts.

> 	fxp_detach()
> [4]	LOCK
> [a]	write 0 to dis intr
> [5]				device B on same intr interrupts here
> 				fxp_intr()
> 				LOCK (->sleep)
> [b]	gone = 0;
> 	UNLOCK
> [1]				if (gone) return;
> [2]	bus_teardown_intr();
> [3]	bus_teardown_intr returns
> 
> 
> [1] and [2] can happen in any order, but you know both of them have
> happened by [3].

This is true regardless of whether or not you have a gone flag.  The
interrupt handler will not be executing by the time bus_teardown_intr()
returns.  This is all that is required.

> The order of [a] and [b] don't really matter because fxp (or anything
> that shares its interrupt) could generate an interrupt after the lock
> is taken out at [4] and you'd still have a fxp_intr sleeping thread.

And that thread can wakeup as soon as you release your lock.  You
simply cannot call bus_teardown_intr() with a lock held.  Ever.

> This might argue for blocking interrupts during a device detach.  I
> think there might be problems with that apprach as well, although I'd
> have to think about it a bit to be sure.

I don't see that there is any problem with the above approach (it is the
same flow as is used by the ahc and ahd driver) but I still don't see why
a gone flag is required.  Just run through the handler as you normally
would in the shared interrupt case.  The handler will exit if written
correctly.

--
Justin