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s390/cio: introduce driver_override on the css bus

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Sometimes, we want to control which of the matching drivers
binds to a subchannel device (e.g. for subchannels we want to
handle via vfio-ccw).

For pci devices, a mechanism to do so has been introduced in
782a985d7a ("PCI: Introduce new device binding path using
pci_dev.driver_override"). It makes sense to introduce the
driver_override attribute for subchannel devices as well, so
that we can easily extend the 'driverctl' tool (which makes
use of the driver_override attribute for pci).

Note that unlike pci we still require a driver override to
match the subchannel type; matching more than one subchannel
type is probably not useful anyway.

Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
This commit is contained in:
Cornelia Huck
2019-06-13 13:08:15 +02:00
committed by Vasily Gorbik
parent dbd66558dd
commit ebc3d17915
3 changed files with 77 additions and 0 deletions
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23
Documentation/ABI/testing/sysfs-bus-css
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@@ -33,3 +33,26 @@ Description: Contains the PIM/PAM/POM values, as reported by the
in sync with the values current in the channel subsystem).
Note: This is an I/O-subchannel specific attribute.
Users: s390-tools, HAL
What: /sys/bus/css/devices/.../driver_override
Date: June 2019
Contact: Cornelia Huck <cohuck@redhat.com>
linux-s390@vger.kernel.org
Description: This file allows the driver for a device to be specified. 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 is specified by writing a string to the
driver_override file (echo vfio-ccw > driver_override) and
may be cleared with an empty string (echo > driver_override).
This returns 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. If no driver with a
matching name is currently loaded in the kernel, the device
will not bind to any driver. This also allows devices to
opt-out of driver binding using a driver_override name such as
"none". Only a single driver may be specified in the override,
there is no support for parsing delimiters.
Note that unlike the mechanism of the same name for pci, this
file does not allow to override basic matching rules. I.e.,
the driver must still match the subchannel type of the device.