RE: [PATCH] virtio_pci: use irq to detect interrupt support

[Angus Chen]

Hi Mst

> -----Original Message-----
> From: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Sent: Thursday, October 13, 2022 6:04 AM
> To: linux-kernel@xxxxxxxxxxxxxxx
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>; Michael Ellerman
> <mpe@xxxxxxxxxxxxxx>; Angus Chen <angus.chen@xxxxxxxxxxxxxxx>; Jason
> Wang <jasowang@xxxxxxxxxx>; virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Subject: [PATCH] virtio_pci: use irq to detect interrupt support
> 
> 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().
> 
> However Linus said:
> 	The correct way to check for "no irq" doesn't use NO_IRQ at all, it just does
> 		if (dev->irq) ...
> so let's just check irq and be done with it.
> 
> Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Reported-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Fixes: 71491c54eafa ("virtio_pci: don't try to use intxif pin is zero")
> Cc: "Angus Chen" <angus.chen@xxxxxxxxxxxxxxx>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> 
> Build tested only - very late here. Angus any chance you could
> help test this? Thanks!
I tested the patch ，it work well on x86。Inlcude legacy and modern driver.
And I tested it on arm server also，and find some problem because of 0.9.5 limitation.
 "platform bug: legacy virtio-pci must not be used with RAM above 0x%llxGB\n",
 But the error is not effected by our patch.with or without our patch ,it print the same.
And I test modern dirver,it work well also.
Sorry for the late reply.
> 
>  drivers/virtio/virtio_pci_common.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_pci_common.c
> b/drivers/virtio/virtio_pci_common.c
> index 4df77eeb4d16..a6c86f916dbd 100644
> --- a/drivers/virtio/virtio_pci_common.c
> +++ b/drivers/virtio/virtio_pci_common.c
> @@ -409,8 +409,8 @@ 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? If not give up. */
> +	if (!(to_vp_device(vdev)->pci_dev->irq))
>  		return err;
>  	/* Finally fall back to regular interrupts. */
>  	return vp_find_vqs_intx(vdev, nvqs, vqs, callbacks, names, ctx);
> --
> MST