On 03/22/2010 10:35 AM, Michael Tokarev wrote:
Paul Brook wrote at Wed, 17 Mar 2010 11:18:09 +0000:
Oh, well, yes, I remember. qemu is more strict on ISA irq sharing now.
A bit too strict.
/me goes dig out a old patch which never made it upstream for some
reason I forgot. Attached.
This is wrong. Two devices should never be manipulating the same qemu_irq
object. If you want multiple devices connected to the same IRQ then you need
an explicit multiplexer. e.g. arm_timer.c:sp804_set_irq.
So... what we have to do here?
I've looked at the mentioned routine, here it is:
/* Merge the IRQs from the two component devices. */
static void sp804_set_irq(void *opaque, int irq, int level)
{
sp804_state *s = (sp804_state *)opaque;
s->level[irq] = level;
qemu_set_irq(s->irq, s->level[0] || s->level[1]);
}
But I know nothing about qemu internals, so don't quite
understand how to do this in case of serial ports. I
see it is tracking two timers and raises the irq level
if at least one half is raised... That to say - I've
got the idea, but how to apply it to serial ports?
Two devices have the same s->irq. Give each on its own qemu_irq, and
feed it into a multiplexer that ORs them together and sends the result
to the interrupt controller's qemu_irq:
S1 ----qemu_irq---->+------+
| mux +---qemu_irq-----> irq controller
S2 ----qemu_irq---->+------+
(the ascii art will come out all wrong, I know it)
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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