On Tue, Apr 01, 2014 at 10:28:54AM -0600, Alex Williamson wrote: > 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 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, ex: > > 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@xxxxxxxxxx> > --- > > Apologies for the exceptionally long cc list, this is a follow-up to > Stuart's "Subject: mechanism to allow a driver to bind to any device" > thread. This is effectively a v2 of the proof-of-concept patch I > posted in that thread. This version changes to use a dummy id struct > to return on an "override" match, which removes the collateral damage > and greatly simplifies the patch. This feels fairly well baked for > PCI and I would expect that platform drivers could do a similar > implementation. From there perhaps we can discuss whether there's > any advantage to placing driver_override on struct device. The logic > for incorporating it into the match still needs to happen per bus > driver, so it might only contribute to consistency of the show/store > sysfs attributes to move it up to struct device. Please comment. > Thanks, > > Alex > > drivers/pci/pci-driver.c | 25 ++++++++++++++++++++++--- > drivers/pci/pci-sysfs.c | 40 ++++++++++++++++++++++++++++++++++++++++ > include/linux/pci.h | 1 + > 3 files changed, 63 insertions(+), 3 deletions(-) No Documentation/ABI/ update to reflect the ABI you are creating? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
