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

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Message-ID: <20250318115832.04abbea7.alex.williamson@redhat.com>
Date: Tue, 18 Mar 2025 11:58:32 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: Shivaprasad G Bhat <sbhat@...ux.ibm.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 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()?  We don't allow a zero irq to be enabled in
vfio_intx_enable(), so we might as well not report it as supported.  I
don't see why any of this needs to be POWER specific.  Thanks,

Alex