Re: [RFC QEMU PATCH v3 1/1] xen: Use gsi instead of irq for mapping pirq

[Chen, Jiqian]

On 2023/12/11 23:33, Roger Pau Monné wrote:
> On Mon, Dec 11, 2023 at 12:52:40AM +0800, Jiqian Chen wrote:
>> In PVH dom0, it uses the linux local interrupt mechanism,
>> when it allocs irq for a gsi, it is dynamic, and follow
>> the principle of applying first, distributing first. And
>> the irq number is alloced from small to large, but the
>> applying gsi number is not, may gsi 38 comes before gsi
>> 28, that causes the irq number is not equal with the gsi
>> number. And when passthrough a device, qemu wants to use
>> gsi to map pirq, xen_pt_realize->xc_physdev_map_pirq, but
>> the gsi number is got from file
>> /sys/bus/pci/devices/<sbdf>/irq in current code, so it
>> will fail when mapping.
>>
>> Use real gsi number read from gsi sysfs.
>>
>> Co-developed-by: Huang Rui <ray.huang@amd.com>
>> Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
>> ---
>>  hw/xen/xen-host-pci-device.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/xen/xen-host-pci-device.c b/hw/xen/xen-host-pci-device.c
>> index 8c6e9a1716..e270ac2631 100644
>> --- a/hw/xen/xen-host-pci-device.c
>> +++ b/hw/xen/xen-host-pci-device.c
>> @@ -364,7 +364,7 @@ void xen_host_pci_device_get(XenHostPCIDevice *d, 
>> uint16_t domain,
>>      }
>>      d->device_id = v;
>>  
>> -    xen_host_pci_get_dec_value(d, "irq", &v, errp);
>> +    xen_host_pci_get_dec_value(d, "gsi", &v, errp);
> 
> Don't you need to fallthrough to use the irq number on failure?
> Otherwise passthrough won't work on older Linux versions that don't
> expose the gsi node.
You are right, I will use the irq if there isn't a gsi sysfs, in next version. 
Thank you.

> 
> Thanks, Roger.

-- 
Best regards,
Jiqian Chen.