linux-kernel - Re: [PATCH] vfio: pci: Advertise INTx only if LINE is connected

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Message-ID: <9131d1be-d68e-48d6-afe3-af8949194b21@linux.ibm.com>
Date: Thu, 20 Mar 2025 23:24:49 +0530
From: Shivaprasad G Bhat <sbhat@...ux.ibm.com>
To: Alex Williamson <alex.williamson@...hat.com>
Cc: jgg@...pe.ca, kevin.tian@...el.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, yi.l.liu@...el.com, Yunxiang.Li@....com,
        pstanner@...hat.com, maddy@...ux.ibm.com,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] vfio: pci: Advertise INTx only if LINE is connected

On 3/18/25 11:28 PM, Alex Williamson wrote:
> On Tue, 18 Mar 2025 17:29:21 +0000
> Shivaprasad G Bhat <sbhat@...ux.ibm.com> wrote:
>
>> On POWER systems, when the device is behind the io expander,
>> not all PCI slots would have the PCI_INTERRUPT_LINE connected.
>> The firmware assigns a valid PCI_INTERRUPT_PIN though. In such
>> configuration, the irq_info ioctl currently advertizes the
>> irq count as 1 as the PCI_INTERRUPT_PIN is valid.
>>
>> The patch adds the additional check[1] if the irq is assigned
>> for the PIN which is done iff the LINE is connected.
>>
>> [1]: https://lore.kernel.org/qemu-devel/20250131150201.048aa3bf.alex.williamson@redhat.com/
>>
>> Signed-off-by: Shivaprasad G Bhat <sbhat@...ux.ibm.com>
>> Suggested-By: Alex Williamson <alex.williamson@...hat.com>
>> ---
>>   drivers/vfio/pci/vfio_pci_core.c |    4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
>> index 586e49efb81b..4ce70f05b4a8 100644
>> --- a/drivers/vfio/pci/vfio_pci_core.c
>> +++ b/drivers/vfio/pci/vfio_pci_core.c
>> @@ -734,6 +734,10 @@ static int vfio_pci_get_irq_count(struct vfio_pci_core_device *vdev, int irq_typ
>>   			return 0;
>>   
>>   		pci_read_config_byte(vdev->pdev, PCI_INTERRUPT_PIN, &pin);
>> +#if IS_ENABLED(CONFIG_PPC64)
>> +		if (!vdev->pdev->irq)
>> +			pin = 0;
>> +#endif
>>   
>>   		return pin ? 1 : 0;
>>   	} else if (irq_type == VFIO_PCI_MSI_IRQ_INDEX) {
>>
>>
> See:
>
> https://lore.kernel.org/all/20250311230623.1264283-1-alex.williamson@redhat.com/
>
> Do we need to expand that to test !vdev->pdev->irq in
> vfio_config_init()?

Yes. Looks to be the better option. I did try this and it works.


I see your patch has already got Reviewed-by. Are you planning

for v2 Or want me to post a separate patch with this new check?


> We don't allow a zero irq to be enabled in
> vfio_intx_enable(), so we might as well not report it as supported.

Yes. I agree.


Thank you!


Regards,

Shivaprasad