The VIA intergrated south bridge chips combine several functions and
allow routing their interrupts to any of the ISA IRQs (also allowing
multiple components to share the same ISA IRQ, e.g. pegasos2 firmware
configures USB, sound and PCI to all use IRQ 9). Bring back
via_isa_set_irq() and change it to take the PCIDevice that wants to
change an IRQ and keep track of the interrupt status of each source
separately and do the mapping to ISA IRQ within the ISA bridge to
allow different sources to control the same ISA IRQ lines.

This may not handle cases when the ISA IRQ is also controlled by
devices directly, not going through via_isa_set_irq() such as serial,
parallel or keyboard but these IRQs being conventionally fixed are not
likely for guests to change or share with other devices so hopefully
this does not cause a problem in practice.

This reverts commit 4e5a20b6da9b1f6d2e9621ed7eb8b239560104ae.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
---
 hw/isa/vt82c686.c         | 39 +++++++++++++++++++++++++++++++++++++++
 include/hw/isa/vt82c686.h |  2 ++
 2 files changed, 41 insertions(+)

diff --git a/hw/isa/vt82c686.c b/hw/isa/vt82c686.c
index 57bdfb4e78..c1826c77eb 100644
--- a/hw/isa/vt82c686.c
+++ b/hw/isa/vt82c686.c
@@ -549,6 +549,7 @@ struct ViaISAState {
     PCIDevice dev;
     qemu_irq cpu_intr;
     qemu_irq *isa_irqs_in;
+    uint16_t isa_irq_state[ISA_NUM_IRQS];
     ViaSuperIOState via_sio;
     MC146818RtcState rtc;
     PCIIDEState ide;
@@ -592,6 +593,44 @@ static const TypeInfo via_isa_info = {
     },
 };
 
+void via_isa_set_irq(PCIDevice *d, int pin, int level)
+{
+    ViaISAState *s = VIA_ISA(pci_get_function_0(d));
+    int n = PCI_FUNC(d->devfn);
+    uint8_t isa_irq = d->config[PCI_INTERRUPT_LINE], max_irq = 15;
+
+    switch (n) {
+    case 2: /* USB ports 0-1 */
+    case 3: /* USB ports 2-3 */
+        max_irq = 14;
+        break;
+    }
+
+    if (unlikely(isa_irq > max_irq || isa_irq == 2)) {
+        qemu_log_mask(LOG_GUEST_ERROR, "Invalid ISA IRQ routing %d for %d",
+                      isa_irq, n);
+        return;
+    }
+    if (isa_irq == 0) {
+        return; /* disabled */
+    }
+
+    /*
+     * In addition to recording status of sources mapped to each isa_irq we
+     * keep track of all sources in IRQ 0 and use that as a mask to avoid stuck
+     * interrupts in case mapping of a source is changed while IRQ is raised.
+     */
+    if (level) {
+        s->isa_irq_state[isa_irq] |= BIT(n);
+        s->isa_irq_state[0] |= BIT(n);
+    } else {
+        s->isa_irq_state[isa_irq] &= ~BIT(n);
+        s->isa_irq_state[0] &= ~BIT(n);
+    }
+    s->isa_irq_state[isa_irq] &= s->isa_irq_state[0];
+    qemu_set_irq(s->isa_irqs_in[isa_irq], !!s->isa_irq_state[isa_irq]);
+}
+
 static void via_isa_request_i8259_irq(void *opaque, int irq, int level)
 {
     ViaISAState *s = opaque;
diff --git a/include/hw/isa/vt82c686.h b/include/hw/isa/vt82c686.h
index b6e95b2851..da1722daf2 100644
--- a/include/hw/isa/vt82c686.h
+++ b/include/hw/isa/vt82c686.h
@@ -34,4 +34,6 @@ struct ViaAC97State {
     uint32_t ac97_cmd;
 };
 
+void via_isa_set_irq(PCIDevice *d, int n, int level);
+
 #endif
-- 
2.30.9

On Sun, 29 Oct 2023, BALATON Zoltan wrote:
> The VIA intergrated south bridge chips combine several functions and
> allow routing their interrupts to any of the ISA IRQs (also allowing
> multiple components to share the same ISA IRQ, e.g. pegasos2 firmware
> configures USB, sound and PCI to all use IRQ 9). Bring back
> via_isa_set_irq() and change it to take the PCIDevice that wants to
> change an IRQ and keep track of the interrupt status of each source
> separately and do the mapping to ISA IRQ within the ISA bridge to
> allow different sources to control the same ISA IRQ lines.
>
> This may not handle cases when the ISA IRQ is also controlled by
> devices directly, not going through via_isa_set_irq() such as serial,
> parallel or keyboard but these IRQs being conventionally fixed are not
> likely for guests to change or share with other devices so hopefully
> this does not cause a problem in practice.
>
> This reverts commit 4e5a20b6da9b1f6d2e9621ed7eb8b239560104ae.
>
> Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
> ---
> hw/isa/vt82c686.c         | 39 +++++++++++++++++++++++++++++++++++++++
> include/hw/isa/vt82c686.h |  2 ++
> 2 files changed, 41 insertions(+)
>
> diff --git a/hw/isa/vt82c686.c b/hw/isa/vt82c686.c
> index 57bdfb4e78..c1826c77eb 100644
> --- a/hw/isa/vt82c686.c
> +++ b/hw/isa/vt82c686.c
> @@ -549,6 +549,7 @@ struct ViaISAState {
>     PCIDevice dev;
>     qemu_irq cpu_intr;
>     qemu_irq *isa_irqs_in;
> +    uint16_t isa_irq_state[ISA_NUM_IRQS];
>     ViaSuperIOState via_sio;
>     MC146818RtcState rtc;
>     PCIIDEState ide;
> @@ -592,6 +593,44 @@ static const TypeInfo via_isa_info = {
>     },
> };
>
> +void via_isa_set_irq(PCIDevice *d, int pin, int level)
> +{
> +    ViaISAState *s = VIA_ISA(pci_get_function_0(d));
> +    int n = PCI_FUNC(d->devfn);
> +    uint8_t isa_irq = d->config[PCI_INTERRUPT_LINE], max_irq = 15;
> +
> +    switch (n) {
> +    case 2: /* USB ports 0-1 */
> +    case 3: /* USB ports 2-3 */
> +        max_irq = 14;
> +        break;
> +    }
> +
> +    if (unlikely(isa_irq > max_irq || isa_irq == 2)) {
> +        qemu_log_mask(LOG_GUEST_ERROR, "Invalid ISA IRQ routing %d for %d",
> +                      isa_irq, n);
> +        return;
> +    }
> +    if (isa_irq == 0) {
> +        return; /* disabled */
> +    }
> +
> +    /*
> +     * In addition to recording status of sources mapped to each isa_irq we
> +     * keep track of all sources in IRQ 0 and use that as a mask to avoid stuck
> +     * interrupts in case mapping of a source is changed while IRQ is raised.
> +     */
> +    if (level) {
> +        s->isa_irq_state[isa_irq] |= BIT(n);
> +        s->isa_irq_state[0] |= BIT(n);
> +    } else {
> +        s->isa_irq_state[isa_irq] &= ~BIT(n);
> +        s->isa_irq_state[0] &= ~BIT(n);
> +    }
> +    s->isa_irq_state[isa_irq] &= s->isa_irq_state[0];

Thinking about it some more it still does not catch the case when IRQ is 
still raised so this could temporarly raise the old IRQ as well so maybe 
we can just drop this and go with the v1 of the series. That works well 
enough becuase in practice guests don't change these often, only at boot 
so probably there are no pending interrupts yet so this may not be an 
issue. If we find it is then the proper fix should be adding a PCI config 
write func to every source and clear the old interrupt with 
via_isa_set_irq before changing the PCI_INTERRUPT_LINE value but I don't 
think it's worth implementing that now until we find something that 
it would fix. So ignore this v2 and take the v1 instead.

Regards,
BALATON Zoltan

> +    qemu_set_irq(s->isa_irqs_in[isa_irq], !!s->isa_irq_state[isa_irq]);
> +}
> +
> static void via_isa_request_i8259_irq(void *opaque, int irq, int level)
> {
>     ViaISAState *s = opaque;
> diff --git a/include/hw/isa/vt82c686.h b/include/hw/isa/vt82c686.h
> index b6e95b2851..da1722daf2 100644
> --- a/include/hw/isa/vt82c686.h
> +++ b/include/hw/isa/vt82c686.h
> @@ -34,4 +34,6 @@ struct ViaAC97State {
>     uint32_t ac97_cmd;
> };
>
> +void via_isa_set_irq(PCIDevice *d, int n, int level);
> +
> #endif
>