virtio_pci: add module param to force legacy mode

If set, try legacy interface first, modern one if that fails.  Useful to
work around device/driver bugs, and for compatibility testing.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
index 8ae34a3..e894eb2 100644 (file)
--- a/drivers/virtio/virtio_pci_common.c
+++ b/drivers/virtio/virtio_pci_common.c
@@ -19,6 +19,14 @@
 
 #include "virtio_pci_common.h"
 
+static bool force_legacy = false;
+
+#if IS_ENABLED(CONFIG_VIRTIO_PCI_LEGACY)
+module_param(force_legacy, bool, 0444);
+MODULE_PARM_DESC(force_legacy,
+                "Force legacy mode for transitional virtio 1 devices");
+#endif
+
 /* wait for pending irq handlers */
 void vp_synchronize_vectors(struct virtio_device *vdev)
 {
@@ -505,11 +513,20 @@ static int virtio_pci_probe(struct pci_dev *pci_dev,
        if (rc)
                goto err_request_regions;
 
-       rc = virtio_pci_modern_probe(vp_dev);
-       if (rc == -ENODEV)
+       if (force_legacy) {
                rc = virtio_pci_legacy_probe(vp_dev);
-       if (rc)
-               goto err_probe;
+               /* Also try modern mode if we can't map BAR0 (no IO space). */
+               if (rc == -ENODEV || rc == -ENOMEM)
+                       rc = virtio_pci_modern_probe(vp_dev);
+               if (rc)
+                       goto err_probe;
+       } else {
+               rc = virtio_pci_modern_probe(vp_dev);
+               if (rc == -ENODEV)
+                       rc = virtio_pci_legacy_probe(vp_dev);
+               if (rc)
+                       goto err_probe;
+       }
 
        pci_set_master(pci_dev);