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

Sudeep Holla
2025-11-26T14:31:45Z

On Wed, Nov 05, 2025 at 11:49:38AM +0000, Punit Agrawal wrote:
> Hi Sudeep,
>
> Sudeep Holla <sudeep.holla@arm.com> writes:
>
> > 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.
>
> I was interested in taking a closer look at the patches here but they
> have a dependency on support for the telemetry protocol patches. I get a
> compile error.
>
> I was wondering if you have a branch with the dependencies included. Are
> the v1 telemetry support patches[0] the right version to be using?
>

I can create one but that is not strictly necessary. As mentioned in the
cover letter, the only dependency is on value of SCMI_PROTOCOL_TELEMETRY
ins `scmi_std_protocol` enumeration. Just add one and you must be able to
compile the series independent of Cristian series.

--
Regards,
Sudeep