Messages in this thread | | | From | Stuart Yoder <> | Subject | RE: [PATCH] PCI: Introduce new device binding path using pci_dev.driver_override | Date | Thu, 10 Apr 2014 19:30:32 +0000 |
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> -----Original Message----- > From: Alex Williamson [mailto:alex.williamson@redhat.com] > Sent: Friday, April 04, 2014 3:19 PM > To: bhelgaas@google.com; linux-pci@vger.kernel.org > Cc: agraf@suse.de; kvm@vger.kernel.org; konrad.wilk@oracle.com; > kim.phillips@linaro.org; gregkh@linuxfoundation.org; Yoder Stuart-B08248; > linux-kernel@vger.kernel.org; libvir-list@redhat.com; iommu@lists.linux- > foundation.org; tech@virtualopensystems.com; > kvmarm@lists.cs.columbia.edu; christoffer.dall@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.williamson@redhat.com> > ---
Reviewed-by: Stuart Yoder <stuart.yoder@freescale.com>
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