[PATCH v5 0/5] i3c: add i3cdev module to expose i3c dev in /dev

[Sam Agazaryan <samagazaryan@google.com>]

This patch series introduces the i3cdev module, exposing unbound I3C
target devices to userspace via character device nodes (/dev/bus/i3c/*),
along with the i3ctransfer userspace utility in tools/i3c/.

Userspace access to I3C targets is needed for devices that do not have a
kernel driver bound to them, such as targets in ROM/bootloader recovery
mode (e.g., OCP Secure Firmware Recovery v1.1 and Caliptra Silicon Root of
Trust recovery flows), as well as hardware bring-up and diagnostics.

When a kernel driver later binds to an I3C device (for example via
dynamic module loading), i3cdev automatically detaches via the
BUS_NOTIFY_BIND_DRIVER notifier so kernel drivers always take
precedence.

Testing status:
This v5 series has been compile-tested across all modified I3C controller
drivers with W=1. Posting v5 now so collaborators and controller owners
can test the unified UAPI and actual_len updates on their respective
hardware and provide Tested-by tags while we complete final hardware
verification of the v5 updates on our platform.

Changes in v5:
- Updated Patch 2/5 ("i3c: master: add i3c_for_each_dev helper"):
  - Dropped mutex_lock(&i3c_core_lock) around bus_for_each_dev() to avoid
    lock inversion and deadlock with external callbacks (sashiko-bot).
- Added Patch 3/5 ("i3c: use actual_len for read transfers"):
  - Clarified @actual_len kerneldoc in <linux/i3c/device.h>
    (Adrian Hunter).
  - Incorporated Meagan Lloyd's controller updates (adi, dw, cdns,
    mipi-i3c-hci, renesas) so all I3C controller drivers populate
    xfer->actual_len on reads without mutating xfer->len
    (Adrian Hunter, Meagan Lloyd).
  - Updated mctp-i3c to read xfer.actual_len instead of xfer.len
    (Adrian Hunter).
- Updated Patch 4/5 ("i3c: add i3cdev module to expose i3c dev in /dev"):
  - Unified the UAPI around struct i3c_ioc_xfer and I3C_IOC_XFER(N) in
    <uapi/linux/i3c/i3cdev.h>, supporting both SDR and HDR modes via a
    mode field and union { __u8 rnw; __u8 cmd; } (Frank Li).
  - Added __u16 actual_len to struct i3c_ioc_xfer and updated
    i3cdev_do_xfer() to copy actual_len bytes to userspace and write
    actual_len back to userspace via put_user() on read transfers
    (Adrian Hunter, Frank Li).
  - Tracked active i3cdev instances in a private list (i3cdev_list)
    instead of using i3cdev_set_drvdata()/i3cdev_get_drvdata() so i3cdev
    never clobbers client drivers' dev->driver_data (Meagan Lloyd).
  - Validated direction field and verified that reserved padding pad[2] is
    zeroed (Greg KH).
  - Clamped read()/write() byte count to type_max(xfers.len) (u16) to
    prevent silent integer truncation and unbounded kernel allocations
    (sashiko-bot).
  - Used ida_alloc_max() capped to MINORMASK to prevent minor number
    overflow (sashiko-bot).
  - Added i3cdev_attach_lock mutex and idempotency check in
    i3cdev_attach()/i3cdev_detach() to serialize concurrent attach/detach
    calls (sashiko-bot).
  - Updated bus notifier to handle BUS_NOTIFY_DRIVER_NOT_BOUND and return
    NOTIFY_OK instead of raw errno values (sashiko-bot).
- Added Patch 5/5 ("tools: i3c: add i3ctransfer utility"):
  - Added tools/i3c/i3ctransfer.c (adapted from Vitor Soares's
    i3c-tools) updated for struct i3c_ioc_xfer, supporting SDR and HDR
    (-m, -c) modes and reporting actual_len bytes on reads
    (Wolfram Sang).
  - Note to Vitor Soares: Since your original i3ctransfer commit in
    i3c-tools did not include a Signed-off-by tag, could you please
    reply with your Signed-off-by / Acked-by for Patch 5/5?

Changes in v4:
- Dropped dev_open count tracking and used cdev_device_add/del with
  mutex locking to prevent use-after-free on detach
  (Greg KH, Wolfram Sang).
- Fixed 32/64-bit UAPI alignment and added compat_ptr_ioctl.
- Switched to dynamic minor allocation via IDA.

Sam Agazaryan (2):
  i3c: use actual_len for read transfers
  tools: i3c: add i3ctransfer utility

Vitor Soares (3):
  i3c: master: export i3c_masterdev_type
  i3c: master: add i3c_for_each_dev helper
  i3c: add i3cdev module to expose i3c dev in /dev

 MAINTAINERS                            |   2 +
 drivers/i3c/Kconfig                    |  11 +
 drivers/i3c/Makefile                   |   1 +
 drivers/i3c/i3cdev.c                   | 491 +++++++++++++++++++++++++
 drivers/i3c/internals.h                |   4 +
 drivers/i3c/master.c                   |   9 +-
 drivers/i3c/master/adi-i3c-master.c    |   5 +-
 drivers/i3c/master/dw-i3c-master.c     |   2 +-
 drivers/i3c/master/i3c-master-cdns.c   |   5 +-
 drivers/i3c/master/mipi-i3c-hci/core.c |   2 +-
 drivers/i3c/master/renesas-i3c.c       |   3 +
 drivers/net/mctp/mctp-i3c.c            |  10 +-
 include/linux/i3c/device.h             |   2 +-
 include/uapi/linux/i3c/i3cdev.h        |  57 +++
 tools/Makefile                         |  13 +-
 tools/i3c/Build                        |   1 +
 tools/i3c/Makefile                     |  58 +++
 tools/i3c/i3ctransfer.c                | 307 ++++++++++++++++
 18 files changed, 966 insertions(+), 17 deletions(-)
 create mode 100644 drivers/i3c/i3cdev.c
 create mode 100644 include/uapi/linux/i3c/i3cdev.h
 create mode 100644 tools/i3c/Build
 create mode 100644 tools/i3c/Makefile
 create mode 100644 tools/i3c/i3ctransfer.c

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2.55.0.1082.g2b9226bbc0-goog