> -----Original Message----- > From: Alex Williamson [mailto:alex.william...@redhat.com] > Sent: Friday, April 04, 2014 3:19 PM > To: bhelg...@google.com; linux-...@vger.kernel.org > Cc: ag...@suse.de; k...@vger.kernel.org; konrad.w...@oracle.com; > kim.phill...@linaro.org; gre...@linuxfoundation.org; Yoder Stuart-B08248; > linux-ker...@vger.kernel.org; libvir-list@redhat.com; iommu@lists.linux- > foundation.org; t...@virtualopensystems.com; > kvm...@lists.cs.columbia.edu; christoffer.d...@linaro.org > Subject: [PATCH] PCI: Introduce new device binding path using > pci_dev.driver_override > > The driver_override field allows us to specify the driver for a device > rather than relying on the driver to provide a positive match of the > device. This shortcuts the existing process of looking up the vendor > and device ID, adding them to the driver new_id, binding the device, > then removing the ID, but it also provides a couple advantages. > > First, the above existing process allows the driver to bind to any > device matching the new_id for the window where it's enabled. This is > often not desired, such as the case of trying to bind a single device > to a meta driver like pci-stub or vfio-pci. Using driver_override we > can do this deterministically using: > > echo pci-stub > /sys/bus/pci/devices/0000:03:00.0/driver_override > echo 0000:03:00.0 > /sys/bus/pci/devices/0000:03:00.0/driver/unbind > echo 0000:03:00.0 > /sys/bus/pci/drivers_probe > > Previously we could not invoke drivers_probe after adding a device > to new_id for a driver as we get non-deterministic behavior whether > the driver we intend or the standard driver will claim the device. > Now it becomes a deterministic process, only the driver matching > driver_override will probe the device. > > To return the device to the standard driver, we simply clear the > driver_override and reprobe the device: > > echo > /sys/bus/pci/devices/0000:03:00.0/preferred_driver > echo 0000:03:00.0 > /sys/bus/pci/devices/0000:03:00.0/driver/unbind > echo 0000:03:00.0 > /sys/bus/pci/drivers_probe > > Another advantage to this approach is that we can specify a driver > override to force a specific binding or prevent any binding. For > instance when an IOMMU group is exposed to userspace through VFIO > we require that all devices within that group are owned by VFIO. > However, devices can be hot-added into an IOMMU group, in which case > we want to prevent the device from binding to any driver (preferred > driver = "none") or perhaps have it automatically bind to vfio-pci. > With driver_override it's a simple matter for this field to be set > internally when the device is first discovered to prevent driver > matches. > > Signed-off-by: Alex Williamson <alex.william...@redhat.com> > ---
Reviewed-by: Stuart Yoder <stuart.yo...@freescale.com> -- libvir-list mailing list libvir-list@redhat.com https://www.redhat.com/mailman/listinfo/libvir-list
