Subject: [PATCH v6 0/4] Switch Arm SMCCC firmware services to an SMCCC bus

From: "Aneesh Kumar K.V (Arm)" <[email-masked]>
Date: Wed, 27 May 2026 15:32:29 +0530

As discussed here:
https://lore.kernel.org/all/[email-masked]

The earlier CCA guest support used an arm-cca-dev platform device as a pure
software anchor for the TSM class device. That platform device did not
correspond to a DT/ACPI described device, MMIO range, interrupt, or other
platform resource; it existed only to make the CCA guest driver bind and to
place the resulting TSM device in the driver model. The same pattern also
exists for smccc_trng. Creating separate platform devices for such
SMCCC-discovered features is misleading, because those features are not
independent platform devices.

This series adds an Arm SMCCC bus for services discovered through the SMCCC
firmware interface. The bus provides SMCCC device and driver registration
helpers, name-based matching, uevent modalias generation, and a sysfs modalias
attribute. SMCCC service drivers can use MODULE_DEVICE_TABLE(arm_smccc, ...)
to emit arm_smccc:<name> aliases, allowing userspace to autoload service
drivers when the SMCCC core registers matching firmware-service devices.

The series then moves SMCCC TRNG and the Arm CCA guest RSI service off the
platform bus. When the SMCCC core discovers the corresponding firmware
service, it registers an arm-smccc device for that service. The hwrng
arm_smccc_trng driver and the Arm CCA guest TSM provider are converted to
SMCCC drivers that bind to those discovered devices.

The old arm-cca-dev platform device has also been used by userspace as a Realm
guest indicator. Removing it without a replacement would leave userspace
depending on an internal driver-binding device. This series therefore adds
/sys/firmware/cca/realm_guest as a stable, architecture-provided ABI for
detecting whether the kernel is running as an Arm CCA Realm guest, and then
removes the dummy arm-cca-dev platform-device registration.

Changes from v5:
https://lore.kernel.org/all/[email-masked]
* Replace the arm-smccc platform-device plus auxiliary-child model with a
  dedicated Arm SMCCC bus.
* Add SMCCC module alias support so SMCCC service drivers can use
  MODULE_DEVICE_TABLE(arm_smccc, ...) and autoload through arm_smccc:<name>
  aliases.
* Convert smccc_trng from a platform driver to an SMCCC driver.
* Convert the Arm CCA guest TSM provider from the arm-cca-dev platform device
  to an SMCCC driver bound to the discovered RSI service.
* Add /sys/firmware/cca/realm_guest before removing the old arm-cca-dev dummy
  platform device.

Changes from v4:
https://lore.kernel.org/all/[email-masked]
* Add /sys/firmware/cca/realm_guest for detecting realm guest
* Convert smccc_trng to auxiliary device from platform device

Changes from v3:
https://lore.kernel.org/all/[email-masked]
* Rebased onto the latest kernel
* Drop pr_fmt() from drivers/firmware/smccc/rmm.c

Cc: Catalin Marinas <[email-masked]>
Cc: Greg KH <[email-masked]>
Cc: Jeremy Linton <[email-masked]>
Cc: Jonathan Cameron <[email-masked]>
Cc: Lorenzo Pieralisi <[email-masked]>
Cc: Mark Rutland <[email-masked]>
Cc: Sudeep Holla <[email-masked]>
Cc: Will Deacon <[email-masked]>
Cc: Steven Price <[email-masked]>
Cc: Suzuki K Poulose <[email-masked]>

Aneesh Kumar K.V (Arm) (4):
  firmware: smccc: Add an Arm SMCCC bus
  firmware: hwrng: arm_smccc_trng: Register as an SMCCC device
  firmware: smccc: arm-cca-guest: Bind the TSM provider to an SMCCC
    device
  coco: guest: arm64: Replace dummy CCA device with sysfs ABI

 Documentation/ABI/testing/sysfs-firmware-cca  |  10 +
 arch/arm64/include/asm/rsi.h                  |   2 +-
 arch/arm64/kernel/rsi.c                       |  39 +++-
 drivers/char/hw_random/arm_smccc_trng.c       |  26 +--
 drivers/firmware/smccc/Makefile               |   4 +
 drivers/firmware/smccc/rmm.c                  |  25 +++
 drivers/firmware/smccc/rmm.h                  |  17 ++
 drivers/firmware/smccc/smccc.c                | 178 +++++++++++++++++-
 drivers/virt/coco/arm-cca-guest/Kconfig       |   1 +
 drivers/virt/coco/arm-cca-guest/Makefile      |   2 +
 .../{arm-cca-guest.c => arm-cca.c}            |  60 +++---
 include/linux/arm-smccc-bus.h                 |  49 +++++
 include/linux/mod_devicetable.h               |  13 ++
 scripts/mod/devicetable-offsets.c             |   3 +
 scripts/mod/file2alias.c                      |   8 +
 15 files changed, 378 insertions(+), 59 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-firmware-cca
 create mode 100644 drivers/firmware/smccc/rmm.c
 create mode 100644 drivers/firmware/smccc/rmm.h
 rename drivers/virt/coco/arm-cca-guest/{arm-cca-guest.c => arm-cca.c} (85%)
 create mode 100644 include/linux/arm-smccc-bus.h

base-commit: 50897c955902c93ae71c38698abb910525ebdc89
-- 
2.43.0