On Sat, 17 Jan 2009, Michael Schmitz wrote:
Can't you add an empty SCC dispatch that just returns, or will that
cause an interrupt storm?
The VIA would be OK with that. Whether it would work or not would depend
on the SCC. That is, I don't know.
The SCC IRQ isn't a VIA interrupt as far as I can tell. It looks like
If it's not on the same level as one of the VIAs the SCC definitely would be
handling the exception protocol itself. But then, it should have been possible
to specify an interrupt vector for each side - ISTR someone telling me that's
not possible because of how it is hooked up.
only models with OSS (the IIfx) or PSC (Q660AV + Q840AV) have a way
to block the SCC IRQ. The comments in mac_scc_dispatch specifically
say that the SCC causes interrupt storms if we ignore it.
It should still be possible to shut down the SCC - after all, we have the base
address in the bootinfo? Best do that in the early arch init code before
interrupts are turned on.
We really ought to redesign the interrupt handling for macs so it's
obvious how the interrupts wander through all the layers. There is
all that logic in the common m68k interrupt handling to register
different interrupt controllers and the mac code just registers one
giant synthetic interrupt source rather than having each driver
register directly with the core for VIA, OSS, PSC, etc.
You could also ifdef 0 the relevant code in via.c --
311 request_irq(IRQ_AUTO_4, mac_scc_dispatch, IRQ_FLG_LOCK,
312 "scc", mac_scc_dispatch);
I don't really care enough to send a temporary patch upstream since the
serial port is presently only useful to those hacking on the kernel
anyway.
I don't think that will really fix anything, since IRQ_AUTO_* interrupts
aren't really blocked or ignored if you don't register them. They go
directly into the CPU which doesn't have a true IRQ mask.
Right - not registering will only invoke the spurious interrupt handler. The
interrupt has to be disabled in the SCC to prevent the interrupt storm.
Can we just use boilerplate SCC init code on all Mac models for this, or does
OSS/PSC/IOP make life more interesting there?
Michael
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