On 20.05.14 16:53, 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 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/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
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 (override
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>
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Reviewed-by: Alexander Graf <ag...@suse.de>
I suppose Konrad's RB stays as well?
Alex
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