On Tue, 2014-04-01 at 09:47 -0700, Greg KH wrote: > 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? Oops, thanks for the reminder. I'd propose this: diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci index a3c5a66..55ca6e5 100644 --- a/Documentation/ABI/testing/sysfs-bus-pci +++ b/Documentation/ABI/testing/sysfs-bus-pci @@ -250,3 +250,21 @@ Description: valid. For example, writing a 2 to this file when sriov_numvfs is not 0 and not 2 already will return an error. Writing a 10 when the value of sriov_totalvfs is 8 will return an error. + +What: /sys/bus/pci/devices/.../driver_override +Date: April 2014 +Contact: Alex Williamson <alex.williamson@xxxxxxxxxx> +Description: + This file allows the driver for a device to be specified + which will override standard static and dynamic ID matching. + When specified, only a driver with a name matching the value + written to driver_override will have an opportunity to bind + to the device. The override may be cleared by writing an + empty string (ex. echo > driver_override), returning the + device to standard matching rules binding. Writing to + driver_override does not automatically unbind the device from + its current driver or make any attempt to automatically load + the specified driver name. If no driver with a matching name + is currently loaded in the kernel, no match will be found. + This also allows devices to opt-out of driver binding using + a driver_override name such as "none". Thanks, Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
