Re: [PATCH v4 1/4] ppc440_pcix: Improve comment for IRQ mapping

[Peter Maydell]

On Mon, 4 Jan 2021 at 23:23, BALATON Zoltan  wrote:
>
> The code mapping all PCI interrupts to a single CPU IRQ works but is
> not trivial so document it in a comment.
>
> Signed-off-by: BALATON Zoltan 
> ---
>  hw/ppc/ppc440_pcix.c | 11 +--
>  1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/hw/ppc/ppc440_pcix.c b/hw/ppc/ppc440_pcix.c
> index ee952314c8..eb1290ffc8 100644
> --- a/hw/ppc/ppc440_pcix.c
> +++ b/hw/ppc/ppc440_pcix.c
> @@ -415,8 +415,15 @@ static void ppc440_pcix_reset(DeviceState *dev)
>  s->sts = 0;
>  }
>
> -/* All pins from each slot are tied to a single board IRQ.
> - * This may need further refactoring for other boards. */
> +/*
> + * All four IRQ[ABCD] pins from all slots are tied to a single board
> + * IRQ, so our mapping function here maps everything to IRQ 0.
> + * The code in pci_change_irq_level() tracks the number of times
> + * the mapped IRQ is asserted and deasserted, so if multiple devices
> + * assert an IRQ at the same time the behaviour is correct.
> + *
> + * This may need further refactoring for boards that use multiple IRQ lines.
> + */
>  static int ppc440_pcix_map_irq(PCIDevice *pci_dev, int irq_num)
>  {
>  trace_ppc440_pcix_map_irq(pci_dev->devfn, irq_num, 0);
> --

Reviewed-by: Peter Maydell 

thanks
-- PMM

[PATCH v4 1/4] ppc440_pcix: Improve comment for IRQ mapping

[BALATON Zoltan via]

The code mapping all PCI interrupts to a single CPU IRQ works but is
not trivial so document it in a comment.

Signed-off-by: BALATON Zoltan 
---
 hw/ppc/ppc440_pcix.c | 11 +--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/hw/ppc/ppc440_pcix.c b/hw/ppc/ppc440_pcix.c
index ee952314c8..eb1290ffc8 100644
--- a/hw/ppc/ppc440_pcix.c
+++ b/hw/ppc/ppc440_pcix.c
@@ -415,8 +415,15 @@ static void ppc440_pcix_reset(DeviceState *dev)
 s->sts = 0;
 }
 
-/* All pins from each slot are tied to a single board IRQ.
- * This may need further refactoring for other boards. */
+/*
+ * All four IRQ[ABCD] pins from all slots are tied to a single board
+ * IRQ, so our mapping function here maps everything to IRQ 0.
+ * The code in pci_change_irq_level() tracks the number of times
+ * the mapped IRQ is asserted and deasserted, so if multiple devices
+ * assert an IRQ at the same time the behaviour is correct.
+ *
+ * This may need further refactoring for boards that use multiple IRQ lines.
+ */
 static int ppc440_pcix_map_irq(PCIDevice *pci_dev, int irq_num)
 {
 trace_ppc440_pcix_map_irq(pci_dev->devfn, irq_num, 0);
-- 
2.21.3