Re: Patch to add support for SGI's IOC4 chipset

[Jeremy Higdon <jeremy@sgi.com>]

On Wed, Oct 22, 2003 at 08:31:02PM +0200, Bartlomiej Zolnierkiewicz wrote:
> 
> I think there is another bug:
> 
> ...
> 	hwif->hw.ack_intr = &sgiioc4_checkirq;	/* MultiFunction Chip */
> ...
> 
> sgiioc4_clearirq() should be used instead of sgiioc4_checkirq() here,
> because otherwise IRQ won't be cleared.
> 
> In order to do this you must modify sgiioc4_clearirq() slightly,
> just change "return intr_reg;" to "return intr_reg & 0x03;".
> 
> If you wonder why, please look at ide_ack_intr() use in ide-io.c:ide_intr().

Thanks.  I've taken a look at it and have become puzzled.

It looks as though ide_ack_intr normally just "returns" 1 and has no
other effect.  But then I see some ide drivers that also have an ack_intr
routine.  On some (most?) architechtures, it would appear that the ack_intr
routine is not used, since the ide_ack_intr macro will not call it.

In gayle_ack_intr_a4000(), it looks as though all it does is read a
register and return something.  Is that register read supposed to clear
interrupt as a side effect.

So maybe an explicit clear is not needed on most implementations?

jeremy