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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     "Michael S. Tsirkin" <mst@redhat.com>, linux-kernel@vger.kernel.org
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Angus Chen <angus.chen@jaguarmicro.com>,
        Jason Wang <jasowang@redhat.com>,
        virtualization@lists.linux-foundation.org
Subject: Re: [PATCH] virtio_pci: use irq to detect interrupt support
In-Reply-To: <20221012220312.308522-1-mst@redhat.com>
References: <20221012220312.308522-1-mst@redhat.com>
Date:   Thu, 13 Oct 2022 12:34:45 +1100
Message-ID: <877d14mrpm.fsf@mpe.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

"Michael S. Tsirkin" <mst@redhat.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().
>
> 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@linux-foundation.org>
> Reported-by: Michael Ellerman <mpe@ellerman.id.au>
> Fixes: 71491c54eafa ("virtio_pci: don't try to use intxif pin is zero")
> Cc: "Angus Chen" <angus.chen@jaguarmicro.com>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
>
> Build tested only - very late here. Angus any chance you could
> help test this? Thanks!

This works for me on powerpc.

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

cheers

> 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