Re: [PATCH v2 00/10] R-Car X5H Ironhide CPG/MDLC SCMI remapping support

On 7/8/26 12:16 PM, Geert Uytterhoeven wrote:
> 	Hi all,
> 
> TL;DR:
> 
>      Describe hardware in DT, and perform the mapping to SCMI in Linux.
> 
> The Renesas R-Car X5H-based Ironhide board is the first Renesas
> SoC/board combination that implements the ARM System Control and
> Management Interface (SCMI).
> 
> This means Linux can no longer perform various system operations (e.g.
> clock, power domain, and reset control) by accessing the hardware
> directly.  Instead, these operations are abstracted according to various
> SCMI sub-protocols, and Linux has to send messages to an SCMI-compliant
> firmware running on a System Control Processor (SCP).
> More specifically, the R-Car X5H SCP FW SCMI controls access to:
>    1. Core clocks and module clocks,
>    2. Module resets,
>    3. Power domains,
>    4. System power.
> The latter is not relevant for this discussion.
> 
> Using SCMI also has an impact on the board DTS: besides the addition of
> a firmware/scmi node with protocol-specific subnodes, devices using
> SCMI-abstracted system resources now have to refer to these resources
> using resource specifiers containing phandles to the SCMI protocol
> subnodes, and firmware-specific object IDs[1].
> 
> Unfortunately we encountered several issues with this:
>    - The clock, reset, and power domain IDs are not stable by design,
>      causing DT incompatibilities.
>      SCMI requires that the ID space exposed to an agent (i.e. Linux)
>      starts at zero and is contiguous.  Hence any change in system
>      partitioning (Application CPU core vs. Realtime CPU core,
>      virtualization, ...) may mean a renumbering of all SCMI IDs,
>      implying a massive change to the DT.
>    - There may be different SCP firmware lineages, e.g. proprietary and
>      certified variants, and FLOSS variants,
>    - SCMI features may differ across firmware versions,
>    - SCMI may abstract the hardware in a different way, requiring changes
>      in (possibly existing) DT bindings and drivers to support the same
>      hardware with and without SCMI:
>        - E.g. the number of SCMI clocks inputs to a hardware block may
> 	differ from the actual hardware,
>        - E.g. hardware clock inputs may be abstracted as SCMI power
> 	domains (or vice versa), like on Qualcomm SA8255P[2].
>      Experience has taught that not describing the hardware in DT may
>      lead to major issues later.
>    - SCMI does not support the concept of a clock domain, so existing
>      drivers can no longer rely on Runtime PM, but need to be changed to
>      manage functional clocks explicitly,
>    - U-Boot IPL (Initial Program Loader) needs a proper hardware
>      description in DT, not using SCMI.
> 
> This list deliberately ignores ID instability and the need for SCMI
> quirks during development of the SCMI firmware.  While upstream Linux
> must only support sufficiently mature firmware versions, vendor trees
> (e.g. renesas-lts) may still want to support development firmware
> versions.
> 
> During last OSSJ/LPC, Marek Vasut pondered if we could keep our own ID
> lists stable, and perform a mapping to the IDs used by the actual SCMI
> implementation running on the system.  This was also briefly discussed
> at LPC[3].  After some refining of the initial idea, this series takes a
> slightly different approach, by:
>    1. Describing the actual hardware components in DT, plus a minimum
>       SCMI glue,
>    2. Mapping DT hardware descriptions to SCMI-backed objects and
>       abstractions (or replacements, in case they are unusable,
>       unavailable, or too different), in Linux drivers, based on the
>       detected firmware version.
> 
> This has the following advantages:
>    1. The DT ABI is stable,
>    2. DT bindings and drivers for existing hardware blocks do not need to
>       be modified,
>    2. Current and future firmware can be handled in driver code,
>    3. U-Boot IPL can use almost the same DTS; it just needs stripping of
>       SCMI-related nodes and properties.
>    4. If ever needed, the Clock Pulse Generator (CPG) and Module
>       Controller (MDLC) drivers can be extended to program the hardware
>       directly if SCMI is not present,
> 
> This series depends on "[PATCH v2 0/6] R-Car X5H CPG/MDLC support"[4],
> and consists of four parts:
>    1. Patches 1-4 add new interfaces needed by the remapping support,
>    2. Patches 5-6 update the DT bindings for the R-Car X5H Clock Pulse
>       Generator (CPG) and Module Controller (MDLC) blocks,
>    3. Patches 7-8 add SCMI remapping support to the R-Car X5H CPG and
>       MDLC drivers,
>    4. Patches 9-10 enables more SCMI protocols on R-Car X5H Ironhide, and
>       link the CPG and MDLC blocks to their SCMI provider.
> 
> Changes compared to v1[5]:
>    - Drop SCMI quirks and SCMI mapping tables,
>    - Move CPG/MDLC DT bindings and minimal base drivers to a separate
>      series,
>    - Add that SCMI may provide different abstractions,
>    - Add missing asterisk to blank kerneldoc line,
>    - Let scmi_get_base_info() return -EPROBE_DEFER or -EOPNOTSUPP instead
>      of -ENOENT, and propagate these errors in callers,
>    - Fall back to the default support when SCMI support or firmware is
>      not available, or when the detected SCMI firmware version is not
>      supported by the driver,
>    - Improve error message on scmi_get_base_info() failure,
>    - Check if SCMI firmware node is available,
>    - Use reverse xmas ordering in r8a78000_cpg_probe(),
>    - Replace the scmi_*_np members of struct r8a78000_*_priv by local
>      variables in the probe functions, and pass them to the fill_*_map()
>      functions,
>    - Join split short lines,
>    - Move check for supported firmware version up,
>    - Fix DT misindentations,
>    - Add scmi_clk node, as it is no longer added in earlier commits.
> 
> Note that in reponse of feedback on v1, I did try to use SCMI IDs in DT,
> and handle most issues in Linux SCMI drivers and SCMI quirks[6].  While
> the result worked, it did not solve everything in the issues list above.
> 
> Note that this series does not include actual SCMI quirks and CPG/MDLC
> mapping tables, as the SCMI firmware for R-Car X5H is still under
> development.
> 
> For testing, I have pushed this series plus additional work to[7].
> 
> Thanks for your comments!
> 
> [1] Documentation/devicetree/bindings/firmware/arm,scmi.yaml
> [2] "[PATCH net-next v11 1/7] dt-bindings: phy: document the serdes PHY on sa8255p"
>      https://lore.kernel.org/[email protected]
> [3] "Firmware ABI stability" at Linux Plumbers Conference 2025
>      https://lpc.events/event/19/contributions/2153/
> [4] "[PATCH v2 0/6] R-Car X5H CPG/MDLC support"
>      https://lore.kernel.org/[email protected]
> [5] "[PATCH/RFC 00/14] R-Car X5H Ironhide SCMI CPG/MDLC remapping"
>      https://lore.kernel.org/[email protected]
> [6] "[PATCH/RFC 0/9] R-Car X5H Ironhide pure SCMI proof-of-concept"
>      https://lore.kernel.org/[email protected]/
> [7] topic/rcar-x5h-ironhide-scmi-cpg-mdlc-remapping-v2 branch of
>      https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git
> 
> Geert Uytterhoeven (10):
>    firmware: arm_scmi: Add scmi_get_base_info()
>    of: property: fw_devlink: Add support for firmware
>    pmdomain: Make genpd_get_from_provider() public
>    reset: Add reset_controller_get_provider()
>    dt-bindings: clock: renesas,r8a78000-cpg: Add firmware property
>    dt-bindings: power: renesas,r8a78000-mdlc: Add firmware property
>    clk: renesas: r8a78000: Add SCMI remapping support
>    pmdomain: renesas: r8a78000: Add SCMI remapping support
>    arm64: dts: renesas: ironhide: Enable SCMI devpd, sys, clock, and
>      reset
>    arm64: dts: renesas: ironhide: Add CPG/MDLC firmware properties
I think 10/10 did not make it either to my inbox or lore.k.o , but the 
remaining 9 patches look good. Thank you !