[PATCH v2 0/7] driver core/USB/thermal: fix device-tree node reuse

Johan Hovold
2017-06-06T16:00:54Z

This series fixes a few issues related to device-tree node reuse.

It is fairly common for drivers to reuse the device-tree node of a
parent (or other ancestor) device when creating class or bus devices
(e.g. gpio chips, i2c adapters, iio chips, spi masters, serdev, phys,
usb root hubs). But reusing a device-tree node may cause problems *if*
the new device is later probed as for example driver core would
currently attempt to reinitialise an already active associated pinmux
configuration.

[ NB: For most examples above this is currently not a problem as the
devices reusing a node are never probed. ]

Other potential issues include the platform-bus code unconditionally
dropping the device-tree-node reference in its device destructor,
reinitialisation of other bus-managed resources such as clocks, and
(possibly) the recently added DMA-setup in driver core.

Instead of having drivers try to work around this (as is currently done
for USB root hubs), we can allow devices to reuse a device-tree node by
setting a flag in their struct device that can be used by core, bus and
driver code to avoid resources from being over-allocated.

The first two patches fix a device-tree node reference leak for
non-root-hub devices in USB. These were submitted yesterday to the USB
list, but are included here for completeness.

The third and fourth patches add a helper that can be used when reusing
a device-tree node of another device and that specifically sets a new
of_node_reused flag which is then used by driver core to skip the
automatic pinctrl configuration during probe.

The fifth patch removes the pinctrl over-allocation workaround from USB
core, which also had some undesirable side-effects.

The final two patches fix a device-tree node imbalance and
use-after-free in an thermal driver, where a platform device was reusing
the device-tree node of its parent mfd during probe. This would also
prevent the child device from being reprobed (e.g. due to probe
deferral) if the parent node defines a pinctrl configuration.

Note that this series is against 4.12-rc3.

For reference, here is a list of relevant commits leading up to the
current situation:

- [2013-01-22] ab78029ecc34 ("drivers/pinctrl: grab default handles from device core")
- [2016-02-19] 69bec7259853 ("USB: core: let USB device know device node")
- [2016-04-25] dc5878abf49c ("usb: core: move root hub's device node assignment after it is added to bus")
- [2016-10-06] 51fa91475e43 ("usb/core: Added devspec sysfs entry for devices behind the usb hub")
- [2017-03-13] a8c06e407ef9 ("usb: separate out sysdev pointer from usb_bus")
- [2017-04-10] 09515ef5ddad ("of/acpi: Configure dma operations at probe time for platform/amba/pci bus devices")

Greg, I'm not sure how best to handle merging this, but I guess all
could go in through driver-core-next to make handling dependencies
easier even if patches 1,2 and 6 could otherwise be considered for
4.12-rc.

Johan

Changes in v2
- update kernel doc comment (2/7)
- add missing kernel doc comment (3/7)
- add Peter's and Linus's acks (1/7 and 4/7)

Johan Hovold (7):
USB: core: fix device node leak
USB: of: document reference taken by child-lookup helper
driver core: add helper to reuse a device-tree node
driver core: fix automatic pinctrl management
USB: of: fix root-hub device-tree node handling
thermal: max77620: fix device-node reference imbalance
thermal: max77620: fix pinmux conflict on reprobe

drivers/base/core.c | 16 ++++++++++++++++
drivers/base/pinctrl.c | 3 +++
drivers/thermal/max77620_thermal.c | 8 ++++++--
drivers/usb/core/hcd.c | 2 --
drivers/usb/core/of.c | 3 ++-
drivers/usb/core/usb.c | 2 ++
include/linux/device.h | 4 ++++
7 files changed, 33 insertions(+), 5 deletions(-)

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2.13.0