linux-kernel - Re: [PATCH] virtio_pci: read interrupt pin directly

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Date:   Thu, 13 Oct 2022 00:29:04 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Angus Chen <angus.chen@...uarmicro.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] virtio_pci: read interrupt pin directly

"Michael S. Tsirkin" <mst@...hat.com> writes:
> commit 71491c54eafa ("virtio_pci: don't try to use intxif pin is zero")
> breaks virtio_pci on powerpc, when running as a qemu guest.
>
> vp_find_vqs() bails out because pci_dev->pin == 0.
>
> But pci_dev->irq is populated correctly, so vp_find_vqs_intx() would
> succeed if we called it - which is what the code used to do.
>
> This seems to happen because pci_dev->pin is not populated in
> pci_assign_irq().
>
> Which is absolutely a bug in the relevant PCI code, but it
> may also affect other platforms that use of_irq_parse_and_map_pci().
>
> Work around the issue in virtio for now, and let's try to fix
> all affected pci systems and then we can revert this.
>
> Reported-by: Michael Ellerman <mpe@...erman.id.au>
> Fixes: 71491c54eafa ("virtio_pci: don't try to use intxif pin is zero")
> Cc: "Angus Chen" <angus.chen@...uarmicro.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  drivers/virtio/virtio_pci_common.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> index 4df77eeb4d16..6155ea4e7e4b 100644
> --- a/drivers/virtio/virtio_pci_common.c
> +++ b/drivers/virtio/virtio_pci_common.c
> @@ -400,6 +400,7 @@ int vp_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
>  		struct irq_affinity *desc)
>  {
>  	int err;
> +	u8 pin = 0;
>  
>  	/* Try MSI-X with one vector per queue. */
>  	err = vp_find_vqs_msix(vdev, nvqs, vqs, callbacks, names, true, ctx, desc);
> @@ -409,8 +410,13 @@ int vp_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
>  	err = vp_find_vqs_msix(vdev, nvqs, vqs, callbacks, names, false, ctx, desc);
>  	if (!err)
>  		return 0;
> -	/* Is there an interrupt pin? If not give up. */
> -	if (!(to_vp_device(vdev)->pci_dev->pin))
> +	/*
> +	 * Is there an interrupt pin? If not give up.
> +	 * NB: It would seem to be better to use pci_dev->pin - unfortunately
> +	 * not all platforms populate it.
> +	 */
> +	pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &pin);
> +	if (!pin)
>  		return err;
>  	/* Finally fall back to regular interrupts. */
>  	return vp_find_vqs_intx(vdev, nvqs, vqs, callbacks, names, ctx);

Needs the delta below in order to compile.

But with that it fixes the issue for me.

Tested-by: Michael Ellerman <mpe@...erman.id.au>

cheers


diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
index 6155ea4e7e4b..cae134e2573f 100644
--- a/drivers/virtio/virtio_pci_common.c
+++ b/drivers/virtio/virtio_pci_common.c
@@ -415,7 +415,7 @@ int vp_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
 	 * NB: It would seem to be better to use pci_dev->pin - unfortunately
 	 * not all platforms populate it.
 	 */
-	pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &pin);
+	pci_read_config_byte(to_vp_device(vdev)->pci_dev, PCI_INTERRUPT_PIN, &pin);
 	if (!pin)
 		return err;
 	/* Finally fall back to regular interrupts. */