As discussed here:
https://lore.kernel.org/all/20250728135216.48084-12-aneesh.kumar@kernel.org

The generic 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.
Instead, introduce an auxiliary device 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
  Provisioning connections between the platform TSM and device DSM

For the CCA platform, the resulting device hierarchy appears as follows:

# cd /sys/class/tsm/
# ls -al
total 0
drwxr-xr-x  2 root root 0 Jan  1 00:01 .
drwxr-xr-x 23 root root 0 Jan  1 00:00 ..
lrwxrwxrwx  1 root root 0 Jan  1 00:01 tsm0 -> ../../devices/platform/arm-smccc/arm_cca_host.arm-rmi-dev.0/tsm/tsm0

-aneesh