[PATCH v4 0/2] Switch Arm CCA to use an auxiliary device instead of a platform device

[Aneesh Kumar K.V (Arm)]

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

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 v3:
https://lore.kernel.org/all/20260309100507.2303361-1-aneesh.kumar@kernel.org
* Rebased onto the latest kernel
* Drop pr_fmt() from drivers/firmware/smccc/rmm.c

Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Greg KH <gregkh at linuxfoundation.org>
Cc: Jeremy Linton <jeremy.linton at arm.com>
Cc: Jonathan Cameron <jic23 at kernel.org>
Cc: Lorenzo Pieralisi <lpieralisi at kernel.org>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Sudeep Holla <sudeep.holla at arm.com>
Cc: Will Deacon <will at kernel.org>

Aneesh Kumar K.V (Arm) (2):
  firmware: smccc: coco: Manage arm-smccc platform device and CCA
    auxiliary drivers
  coco: guest: arm64: Drop dummy RSI platform device stub

 arch/arm64/include/asm/rsi.h                  |  2 +-
 arch/arm64/kernel/rsi.c                       | 15 -----
 drivers/firmware/smccc/Kconfig                |  1 +
 drivers/firmware/smccc/Makefile               |  1 +
 drivers/firmware/smccc/rmm.c                  | 23 ++++++++
 drivers/firmware/smccc/rmm.h                  | 17 ++++++
 drivers/firmware/smccc/smccc.c                | 14 +++++
 drivers/virt/coco/arm-cca-guest/Kconfig       |  1 +
 drivers/virt/coco/arm-cca-guest/Makefile      |  2 +
 .../{arm-cca-guest.c => arm-cca.c}            | 59 +++++++++----------
 10 files changed, 89 insertions(+), 46 deletions(-)
 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