[PATCH v4 0/8] R-Car X5H Ironhide CPG/MDLC SCMI remapping support

[Geert Uytterhoeven <geert+renesas@glider.be>]

	Hi all,

TL;DR:

    Describe hardware in DT, and perform mapping to abstractions offered
    by 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 DT; it just needs stripping of
     the SCMI node and subnodes,
  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,

Last week I gave a presentation about the issues and our solution at
ELCE2026 in Prague[4].

This series consists of four parts:
  A. Patches 1-2 prepare and add SCMI remapping support to the R-Car X5H
     CPG clock driver,
  B. Patches 3-6 fix and add new interfaces needed for remapping in the
     R-Car X5H MDLC pmdomain driver,
  C. Patch 7 adds SCMI remapping support to the R-Car X5H MDLC pmdomain
     driver,
  D. Patch 8 enables more SCMI protocols on R-Car X5H Ironhide.

Dependencies:
  - C depends on B,
  - D depends on A, B, C, and out-of-tree SCMI quirks.

Changes compared to v3[5]:
  - Remove dependencies by making assumptions and dropping disputed
    items, to move this series forward:
      - Assume all SCMI IDs are stable.
        This let us drop the addition of scmi_get_base_info(), and
	support for handling different ID spaces.
      - Drop the "renesas,scmi-firmware" DT property, and find a device
        node compatible with "arm,scmi" instead.
        This let us drop the addition of fw_devlink support for this
	property, too, but required a new probe deferral fix in the
	pmdomain code: "pmdomain: Make genpd_get_from_provider() return
	-EPROBE_DEFER".
	This will have to be revisited when systems with multiple SCMI
	providers appear.
  - Drop unneeded IS_ERR() check after __clk_get_hw(),
  - Mark scmi_{clk,reset,power}_np __free(device_node),
  - Include initial mapping tables for R-Car X5H SCP FW SDKv4.31.0 and
    later, supporting clocks, power domains, and resets used by serial,
    I2C, and SPI devices.
  - Try SCMI clocks first, and fall back to the default fixed-frequency
    clocks when not available, as recent firmware versions no longer
    restrict access to some bus clocks,
  - Fall back to the non-SCMI defaults when SCMI provider support is
    disabled,
  - Keep RESET_CONTROL_FLAGS_BIT_OPTIONAL clearing in
    __fwnode_reset_control_get(),
  - Return directly in __reset_control_get_from_provider(), instead of
    assigning to a local variable, letting us drop the latter and
    simplify scoped_guard() to plain guard(),
  - Add Reviewed-by,
  - Check for overflow when converting (u64) fwnode args to (uint32_t)
    OF args,
  - Document that reset_control_get_from_provider_exclusive() must not
    be given a reference to a GPIO provider,
  - Let the dummy return ERR_PTR(-ENOTSUPP) instead of NULL,
  - Improve patch description,
  - Let r8a78000_mdlc_attach_dev() return success when the MDLC instance
    is not found, to avoid breaking users referring in DT to an SCMI
    power-domain directly,
  - Extract scmi_get_clk(),
  - Add support for gateable functional clock parents,
  - Propagate all reset failures, as SCP FW SDKv4.28.0 which restricted
    HSCIF0 reset is no longer supported.

Changes compared to v2[6]:
  - New patches:
    "[PATCH v3 06/12] reset: Extract __reset_control_get_from_provider()",
    "[PATCH v3 08/12] clk: renesas: r8a78000: Add clk_hw to clk_map",
  - Move DT binding patches forward in series,
  - Add "renesas" vendor prefix and "scmi-" function prefix to the
    "firmware" property (I still think the vendor property should be
    dropped, or replaced by "arm"),
  - Add "of_" prefix to genpd_get_from_provider(),
  - Replace reset_controller_get_provider() by
    reset_control_get_from_provider_exclusive(),
  - Add kerneldoc,
  - Rebase,
  - Consistently use /* sentinel */ for zero sentinels,
  - Call reset_control_*() APIs instead of internal reset_control_ops
    methods,
  - Rename struct mod_map to struct mod_map_in,
  - Add struct mod_map, which also contains a reset_control pointer,
  - Add fill_mod_map() to obtain all SCMI reset_control structures
    up-front, as one can no longer use lazy look-up,
  - Prefix DEFINE_MDLC_RESET_WRAPPER() parameters with underscores.

Changes compared to v1[7]:
  - 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.

Notes:
  - 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[8].  While
    the result worked, it did not solve everything in the issues list
    above.
  - This series does not include actual SCMI quirks; the SCMI firmware
    for R-Car X5H is still under development.

For testing, I have pushed this series plus additional work to[9].

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/20260629-qcom-sa8255p-emac-v11-1-1b7fb95b51f9@oss.qualcomm.com
[3] "Firmware ABI stability" at Linux Plumbers Conference 2025
    https://lpc.events/event/19/contributions/2153/
[4] "Marrying Device Tree and SCMI" (https://sched.co/2RaWR)
[5] "[PATCH v3 00/12] R-Car X5H Ironhide CPG/MDLC SCMI remapping
     support"
    https://lore.kernel.org/cover.1788338320.git.geert+renesas@glider.be/
[6] "[PATCH v2 00/10] R-Car X5H Ironhide CPG/MDLC SCMI remapping
     support"
    https://lore.kernel.org/cover.1783505329.git.geert+renesas@glider.be
[7] "[PATCH/RFC 00/14] R-Car X5H Ironhide SCMI CPG/MDLC remapping"
    https://lore.kernel.org/cover.1776793163.git.geert+renesas@glider.be
[8] "[PATCH/RFC 0/9] R-Car X5H Ironhide pure SCMI proof-of-concept"
    https://lore.kernel.org/cover.1781171705.git.geert+renesas@glider.be/
[9] topic/rcar-x5h-ironhide-scmi-cpg-mdlc-remapping-v4 branch of
    https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git

Geert Uytterhoeven (8):
  clk: renesas: r8a78000: Add clk_hw to clk_map
  clk: renesas: r8a78000: Add SCMI remapping support
  reset: Extract __reset_control_get_from_provider()
  reset: Add reset_control_get_from_provider_exclusive()
  pmdomain: Make genpd_get_from_provider() return -EPROBE_DEFER
  pmdomain: Make genpd_get_from_provider() public
  pmdomain: renesas: r8a78000: Add SCMI remapping support
  arm64: dts: renesas: ironhide: Enable SCMI devpd, sys, clock, and
    reset

 .../boot/dts/renesas/r8a78000-ironhide.dts    |  19 +
 drivers/clk/renesas/r8a78000-cpg.c            | 217 +++++++--
 drivers/pmdomain/core.c                       |  26 +-
 drivers/pmdomain/renesas/r8a78000-mdlc.c      | 410 +++++++++++++++++-
 drivers/reset/core.c                          | 116 +++--
 include/linux/pm_domain.h                     |   7 +
 include/linux/reset.h                         |   8 +
 7 files changed, 698 insertions(+), 105 deletions(-)

-- 
2.43.0

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds