[PATCH 0/5] platform/chrome: Fix a race when probing drivers

[Tzung-Bi Shih <tzungbi@kernel.org>]

A race is observed when cros_ec_lpc and cros-ec-keyb are all built as
modules.  cros_ec_lpc is cros-ec-keyb's parent.  However, they can be
probed at the same time.

Example:

+ -----------------------------------------------------------------+
| Some init process (e.g. udevd) | deferred_probe_work_func worker |
+ -----------------------------------------------------------------+
| Probe cros-ec-keyb.            |                                 |
| - Decide to defer[1].          |                                 |
|                                | A device bound to a driver[2].  |
| Probe cros_ec_lpc.             |                                 |
| - Init the struct[3].          |                                 |
|                                | Retry cros-ec-keyb from the     |
|                                | deferred list[4].               |
|                                | - Won't defer again as [3].     |
|                                | - Access uninitialized data in  |
|                                |   the struct.                   |
| - Register the device.         |                                 |
+ -----------------------------------------------------------------+

[1] https://elixir.bootlin.com/linux/v6.16/source/drivers/input/keyboard/cros_ec_keyb.c#L707
[2] https://elixir.bootlin.com/linux/v6.16/source/drivers/base/dd.c#L405
[3] https://elixir.bootlin.com/linux/v6.16/source/drivers/platform/chrome/cros_ec_lpc.c#L644
[4] https://elixir.bootlin.com/linux/v6.16/source/drivers/base/dd.c#L418

Note that the device link[5] can't help as in the observed environment,
the devices are already added via device_add()[6].

[5] https://www.kernel.org/doc/html/latest/driver-api/device_link.html#usage
[6] https://elixir.bootlin.com/linux/v6.16/source/drivers/acpi/acpi_platform.c#L177

The series fixes the issue by ensuring the struct is ready for accessing
before continuing to probe cros-ec-keyb.

The 1st - 3rd patches are preparatory steps to allow the per-device lock
can be used even if the struct cros_ec_device is unregistered.

The 4th patch introduces a new flag `registered` and use the lock for
protecting the flag.

The 5th patch defers probe if the struct cros_ec_device is not ready yet.

Tzung-Bi Shih (5):
  platform/chrome: Centralize cros_ec_device allocation
  platform/chrome: Centralize common cros_ec_device initialization
  platform/chrome: cros_ec: Separate initialization from
    cros_ec_register()
  platform/chrome: cros_ec: Add a flag to track registration state
  Input: cros_ec_keyb - Defer probe until parent EC device is registered

 drivers/input/keyboard/cros_ec_keyb.c       |  6 ++
 drivers/platform/chrome/cros_ec.c           | 85 ++++++++++++++-------
 drivers/platform/chrome/cros_ec.h           |  3 +
 drivers/platform/chrome/cros_ec_i2c.c       |  9 +--
 drivers/platform/chrome/cros_ec_ishtp.c     |  6 +-
 drivers/platform/chrome/cros_ec_lpc.c       |  6 +-
 drivers/platform/chrome/cros_ec_proto.c     | 15 ++++
 drivers/platform/chrome/cros_ec_rpmsg.c     |  6 +-
 drivers/platform/chrome/cros_ec_spi.c       |  7 +-
 drivers/platform/chrome/cros_ec_uart.c      |  6 +-
 include/linux/platform_data/cros_ec_proto.h | 18 ++++-
 11 files changed, 103 insertions(+), 64 deletions(-)

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2.51.0.268.g9569e192d0-goog