Subject: Re: [PATCH RFC 0/2] clk: scmi: DT support for SCMI clock rate rounding modes (per‑clock policy)

From: Peng Fan <[email-masked]>
Date: Sat, 4 Apr 2026 09:53:10 +0800

Hi All,

On Fri, Mar 06, 2026 at 02:20:11PM +0800, Peng Fan (OSS) wrote:
>The ARM SCMI specification (DEN0056E) defines rounding‑mode flags for the
>CLOCK_RATE_SET command, allowing a client to request that the firmware
>round a requested clock rate down, up, or autonomously choose the
>closest achievable rate.

Would you please give a look and give some feedback?

Thanks,
Peng

>This series introduces DT support in the SCMI clock provider to carry a
>per‑clock rounding policy from the device tree into the SCMI protocol.
>
>Patch 1 adds dt‑bindings constants for rounding modes:
>ROUND_DOWN, ROUND_UP, ROUND_AUTO.
>
>Patch 2 extends the SCMI clock provider to optionally support
>"#clock-cells = <2>", where the second cell encodes the rounding mode.
>The first consumer that references a given clock latches the per‑clock
>policy. Subsequent consumers of the same clock must specify the same
>mode; otherwise, the request is rejected to avoid non‑deterministic
>behavior. The selected mode is passed through to the SCMI Clock protocol
>and mapped to the corresponding CLOCK_SET_* flag.
>
>Patch 2 includes changes to drivers/clk/clk-scmi.c and drivers/firmware
>arm_scmi/clock.c, it is hard to separate the changes without breaking,
>so I put the changes in one patch.
>
>This design adopts a per‑clock policy model, not per‑consumer. The rounding
>mode is applied by the provider per clock (index).
>All consumers of the same clock must agree on the rounding mode.
>Conflicting per‑consumer requests for the same clock are invalid and
>are rejected during phandle translation.
>
>This avoids silent clobbering and preserves deterministic behavior.
>
>Existing device trees using #clock-cells = <1> continue to work and
>default to ROUND_DOWN, exactly as before.
>
>Signed-off-by: Peng Fan <[email-masked]>
>---
>Peng Fan (2):
>      dt-bindings: clock: Add SCMI clock rounding mode declarations
>      clk: scmi: Add support for two #clock-cells to pass rate rounding mode
>
> drivers/clk/clk-scmi.c            | 62 +++++++++++++++++++++++++++++++++++++--
> drivers/firmware/arm_scmi/clock.c | 15 ++++++++--
> include/dt-bindings/clock/scmi.h  | 13 ++++++++
> include/linux/scmi_protocol.h     |  8 ++++-
> 4 files changed, 92 insertions(+), 6 deletions(-)
>---
>base-commit: 3f9cd19e764b782706dbaacc69e502099cb014ba
>change-id: 20260306-scmi-clk-round-1615258cf0fa
>
>Best regards,
>-- 
>Peng Fan <[email-masked]>
>