[PATCH 0/8] firmware: arm_scmi: Refactoring and enablement of ACPI PCC transport

Sudeep Holla
2025-10-17T13:24:27Z

The SCMI can be utilized in systems using either the FDT or ACPI specification.
While FDT-based systems can natively use SCMI, ACPI-based systems often
need to abstract the functionality provided by SCMI under ASL methods.
So far, there has been no need to support SCMI natively on ACPI systems.

However, with the addition of a few new protocols such as Powercap and Telemetry,
which lack abstractions in the ACPI specification, there is now a need to
run SCMI natively for those use cases.

This patch series introduces ACPI PCC transport support for the Arm SCMI
framework, alongside several foundational refactors and enhancements to
achieve firmware-node neutrality between Device Tree (DT) and ACPI systems.

The key changes include:

1. ACPI/DT abstraction and fwnode transition

Converted the core SCMI code to use `fwnode_handle` instead of DT-specific
structures, ensuring seamless operation across both ACPI and DT
environments. All property lookups, child enumeration, and device
association paths have been updated accordingly.

2. Unified transport registration for ACPI and DT

Extended the SCMI transport driver macros to support ACPI match tables,
enabling transports to probe using ACPI device IDs while maintaining
backward compatibility with DT-only systems.

3. Protocol device initialization and refactoring

Refactored the protocol device creation and validation logic into a new
helper for improved readability and maintainability. Enhanced the
initialization logic to handle ACPI-based SCMI devices without explicit
child fwnodes.

4. Introduction of ACPI PCC transport

Added a new SCMI transport driver leveraging ACPI PCCT (Platform
Communications Channel Table) subspaces via the Linux PCC mailbox
framework. This enables SCMI communication over PCC on ACPI-based
platforms.

Collectively, these changes lay the groundwork for robust SCMI operation on
ACPI platforms, achieving near parity with DT systems where applicable,
while enabling the new PCC transport path for firmware communication.

Note: SCMI will not be run natively for all existing protocols other
than Powercap and Telemetry, as they must continue to use ACPI abstractions.
The ACPI SCMI device document is not hosted publicly yet, but the ACPI
namespace snippet below provides a reference example for reviewing these patches.

There is one dependency on the SCMI Telemetry support posted by Cristian [1].
It is required only for the definition of `SCMI_PROTOCOL_TELEMETRY` in the
`scmi_std_protocol` enumeration.

-->8

Device (SCM0) {
Name(_HID, "ARML0001")
Name (_UID, 0)
Name (_DSD, Package () {
ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), // Device Properties UUID
Package () {
Package(2) {
"arm-arml0001-transport-pcc", // Key
Package () { // Value
1, // Revision
3, // Count
Package(){4, 0, 1}, // PCCT Idx, TransportUID, A2P Common
Package(){7, 1, 0}, // PCCT Idx, TransportUID, A2P Exclusive
Package(){9, 2, 2} // PCCT Idx, TransportUID, P2A Exclusive
} // Value
},
Package(2) {
"arm-arml0001-protocol-pcap", // Key
Package () { // Value
1, // Revision
Package() { // Protocol Exclusive Transport Package
// Empty; A2P Common
},
Package() {} // Protocol Association Package
} // Value
},
Package(2) {
"arm-arml0001-protocol-telemetry", // Key
Package () { // Value
1, // Revision
Package() { // Protocol Exclusive Transport Package
Package (2) {1, 0}, // UID=1; Flags=0; A2P Exclusive
Package (2) {2, 0} // UID=2; Flags=0; P2A Exclusive
},
Package() {} // Protocol Association Package
} // Value
},
} // Device Properties
}) // _DSD
} // SCM0

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
---
Sudeep Holla (8):
firmware: arm_scmi: Set fwnode for the genrated SCMI platform device
firmware: arm_scmi: Extend transport driver macro to support ACPI
firmware: arm_scmi: Convert OF-only paths to generic fwnode in SCMI core
firmware: arm_scmi: Fall back to ACPI HID when "compatible" is absent
firmware: arm_scmi: Pass protocol ID to chan_available() transport callback
firmware: arm_scmi: Refactor protocol device creation logic
firmware: arm_scmi: transport: Add ACPI PCC transport
firmware: arm_scmi: Initialise all protocol devices and transport channels

drivers/firmware/arm_scmi/bus.c | 33 +--
drivers/firmware/arm_scmi/common.h | 33 ++-
drivers/firmware/arm_scmi/driver.c | 173 ++++++-----
drivers/firmware/arm_scmi/transports/Kconfig | 12 +
drivers/firmware/arm_scmi/transports/Makefile | 2 +
drivers/firmware/arm_scmi/transports/mailbox.c | 4 +-
drivers/firmware/arm_scmi/transports/optee.c | 4 +-
drivers/firmware/arm_scmi/transports/pcc.c | 390 +++++++++++++++++++++++++
drivers/firmware/arm_scmi/transports/smc.c | 4 +-
drivers/firmware/arm_scmi/transports/virtio.c | 3 +-
10 files changed, 561 insertions(+), 97 deletions(-)
---
base-commit: 7ea30958b3054f5e488fa0b33c352723f7ab3a2a
change-id: 20251017-acpi_scmi_pcc-e44e1233eae3

--
Regards,
Sudeep