Re: [RFC XEN PATCH 6/6] tools/libs/light: pci: translate irq to gsi

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Sun, Mar 12, 2023 at 03:54:55PM +0800, Huang Rui wrote:
> From: Chen Jiqian <Jiqian.Chen@xxxxxxx>
> 
> Use new xc_physdev_gsi_from_irq to get the GSI number
> 
> Signed-off-by: Chen Jiqian <Jiqian.Chen@xxxxxxx>
> Signed-off-by: Huang Rui <ray.huang@xxxxxxx>
> ---
>  tools/libs/light/libxl_pci.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tools/libs/light/libxl_pci.c b/tools/libs/light/libxl_pci.c
> index f4c4f17545..47cf2799bf 100644
> --- a/tools/libs/light/libxl_pci.c
> +++ b/tools/libs/light/libxl_pci.c
> @@ -1486,6 +1486,7 @@ static void pci_add_dm_done(libxl__egc *egc,
>          goto out_no_irq;
>      }
>      if ((fscanf(f, "%u", &irq) == 1) && irq) {
> +        irq = xc_physdev_gsi_from_irq(ctx->xch, irq);

This is just a shot in the dark, because I don't really have enough
context to understand what's going on here, but see below.

I've taken a look at this on my box, and it seems like on
dom0 the value returned by /sys/bus/pci/devices/SBDF/irq is not
very consistent.

If devices are in use by a driver the irq sysfs node reports either
the GSI irq or the MSI IRQ (in case a single MSI interrupt is
setup).

It seems like pciback in Linux does something to report the correct
value:

root@lcy2-dt107:~# cat /sys/bus/pci/devices/0000\:00\:14.0/irq
74
root@lcy2-dt107:~# xl pci-assignable-add 00:14.0
root@lcy2-dt107:~# cat /sys/bus/pci/devices/0000\:00\:14.0/irq
16

As you can see, making the device assignable changed the value
reported by the irq node to be the GSI instead of the MSI IRQ, I would
think you are missing something similar in the PVH setup (some pciback
magic)?

Albeit I have no idea why you would need to translate from IRQ to GSI
in the way you do in this and related patches, because I'm missing the
context.

Regards, Roger.