[PATCH v3 00/12] R-Car X5H Ironhide CPG/MDLC SCMI remapping support
Geert Uytterhoeven
geert+renesas at glider.be
Wed Sep 2 04:29:16 PDT 2026
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 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 consists of four parts:
1. Patches 1-2 update the DT bindings for the R-Car X5H Clock Pulse
Generator (CPG) and Module Controller (MDLC) blocks,
2. Patches 3-7 add new interfaces needed by the remapping support,
3. Patches 8-10 prepare and add SCMI remapping support to the R-Car
X5H CPG and MDLC drivers,
4. Patches 11-12 enable more SCMI protocols on R-Car X5H Ironhide, and
link the CPG and MDLC blocks to their SCMI provider.
Changes compared to v2[4]:
- 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[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/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] "[PATCH v2 00/10] R-Car X5H Ironhide CPG/MDLC SCMI remapping
support"
https://lore.kernel.org/cover.1783505329.git.geert+renesas@glider.be
[5] "[PATCH/RFC 00/14] R-Car X5H Ironhide SCMI CPG/MDLC remapping"
https://lore.kernel.org/cover.1776793163.git.geert+renesas@glider.be
[6] "[PATCH/RFC 0/9] R-Car X5H Ironhide pure SCMI proof-of-concept"
https://lore.kernel.org/cover.1781171705.git.geert+renesas@glider.be/
[7] topic/rcar-x5h-ironhide-scmi-cpg-mdlc-remapping-v3 branch of
https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git
Geert Uytterhoeven (12):
dt-bindings: clock: renesas,r8a78000-cpg: Add renesas,scmi-firmware
property
dt-bindings: power: renesas,r8a78000-mdlc: Add firmware property
firmware: arm_scmi: Add scmi_get_base_info()
of: property: fw_devlink: Add support for renesas,scmi-firmware
pmdomain: Make genpd_get_from_provider() public
reset: Extract __reset_control_get_from_provider()
reset: Add reset_control_get_from_provider_exclusive()
clk: renesas: r8a78000: Add clk_hw to clk_map
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 renesas,scmi-firmware
properties
.../bindings/clock/renesas,r8a78000-cpg.yaml | 9 +
.../bindings/power/renesas,r8a78000-mdlc.yaml | 9 +
.../boot/dts/renesas/r8a78000-ironhide.dts | 135 ++++++
drivers/clk/renesas/r8a78000-cpg.c | 230 +++++++++--
drivers/firmware/arm_scmi/driver.c | 33 ++
drivers/of/property.c | 2 +
drivers/pmdomain/core.c | 22 +-
drivers/pmdomain/renesas/r8a78000-mdlc.c | 383 ++++++++++++++++--
drivers/reset/core.c | 119 ++++--
include/linux/pm_domain.h | 7 +
include/linux/reset.h | 8 +
include/linux/scmi_protocol.h | 8 +
12 files changed, 859 insertions(+), 106 deletions(-)
--
2.43.0
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at 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
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