Subject: [PATCH v5 0/3] Switch Arm CCA to use an auxiliary device instead of a platform device

From: "Aneesh Kumar K.V (Arm)" <[email-masked]>
Date: Thu, 14 May 2026 15:10:27 +0530

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

The general feedback was that a platform device should not be used when
there is no underlying platform resource to represent. The existing CCA
support uses a platform device solely to anchor the TSM interface in the
device hierarchy, which is not an appropriate use of a platform device.
Use an auxiliary device instead to track CCA support.

The TSM framework uses the device abstraction to provide cross-architecture
TSM and TEE I/O functionality, including enumerating available platform TEE
I/O capabilities and provisioning connections between the platform TSM and
device DSMs.

For the CCA platform, the resulting device hierarchy appears as follows.
Note that the auxiliary device is still parented by the arm-smccc platform
device, so the sysfs path remains under /devices/platform/arm-smccc/:

$ cd /sys/class/tsm/
$ ls -al
total 0
drwxr-xr-x    2 root     root             0 Jan  1 00:02 .
drwxr-xr-x   23 root     root             0 Jan  1 00:00 ..
lrwxrwxrwx    1 root     root             0 Jan  1 00:03 tsm0 -> ../../devices/platform/arm-smccc/arm_cca_guest.arm-rsi-dev.0/tsm/tsm0
$

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) (3):
  firmware: smccc: coco: Manage arm-smccc platform device and CCA
    auxiliary drivers
  hwrng: arm_smccc_trng: Register as an auxiliary 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       | 25 ++++----
 drivers/firmware/smccc/Kconfig                |  1 +
 drivers/firmware/smccc/Makefile               |  1 +
 drivers/firmware/smccc/rmm.c                  | 24 ++++++++
 drivers/firmware/smccc/rmm.h                  | 17 ++++++
 drivers/firmware/smccc/smccc.c                | 29 +++++++--
 drivers/virt/coco/arm-cca-guest/Kconfig       |  1 +
 drivers/virt/coco/arm-cca-guest/Makefile      |  2 +
 .../{arm-cca-guest.c => arm-cca.c}            | 59 +++++++++----------
 12 files changed, 153 insertions(+), 57 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} (84%)

-- 
2.43.0