linux-kernel - [PATCH] virtio_pci: use irq to detect interrupt support

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Message-ID: <20221012220312.308522-1-mst@redhat.com>
Date:   Wed, 12 Oct 2022 18:04:03 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Angus Chen <angus.chen@...uarmicro.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
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@...ux-foundation.org>
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>
---

Build tested only - very late here. Angus any chance you could
help test this? Thanks!

 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