driver core: Move the "removable" attribute from USB to core

Move the "removable" attribute from USB to core in order to allow it to be
supported by other subsystem / buses. Individual buses that want to support
this attribute can populate the removable property of the device while
enumerating it with the 3 possible values -
 - "unknown"
 - "fixed"
 - "removable"
Leaving the field unchanged (i.e. "not supported") would mean that the
attribute would not show up in sysfs for that device. The UAPI (location,
symantics etc) for the attribute remains unchanged.

Move the "removable" attribute from USB to the device core so it can be
used by other subsystems / buses.

By default, devices do not have a "removable" attribute in sysfs.

If a subsystem or bus driver wants to support a "removable" attribute, it
should call device_set_removable() before calling device_register() or
device_add(), e.g.:

    device_set_removable(dev, DEVICE_REMOVABLE);
    device_register(dev);

The possible values and the resulting sysfs attribute contents are:

    DEVICE_REMOVABLE_UNKNOWN  ->  "unknown"
    DEVICE_REMOVABLE          ->  "removable"
    DEVICE_FIXED              ->  "fixed"

Convert the USB "removable" attribute to use this new device core
functionality.  There should be no user-visible change in the location or
semantics of attribute for USB devices.

Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Rajat Jain <rajatja@google.com>
Link: https://lore.kernel.org/r/20210524171812.18095-1-rajatja@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-devices-removable b/Documentation/ABI/testing/sysfs-devices-removable
new file mode 100644
index 000000000000..acf7766e800b
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-devices-removable
@@ -0,0 +1,17 @@
+What:		/sys/devices/.../removable
+Date:		May 2021
+Contact:	Rajat Jain <rajatxjain@gmail.com>
+Description:
+		Information about whether a given device can be removed from the
+		platform by the	user. This is determined by its subsystem in a
+		bus / platform-specific way. This attribute is only present for
+		devices that can support determining such information:
+
+		"removable": device can be removed from the platform by the user
+		"fixed":     device is fixed to the platform / cannot be removed
+			     by the user.
+		"unknown":   The information is unavailable / cannot be deduced.
+
+		Currently this is only supported by USB (which infers the
+		information from a combination of hub descriptor bits and
+		platform-specific data such as ACPI).