ACPM cpufreq with fast_switch support, fast path xfer in ACPM

The series implements acpm_do_xfer_fast() that does as little
as possible to make it usabe in atomic context to eventually
use it in cpufreq path with ->fast_switch(). That's basically it.
Cpufreq deals directly with ACPM dvfs instead of going through
clk framework.

This series is Work-In-Progress / RFC.
This is currently a working prototype, but I am sending it as an RFC to
get feedback on the approach — specifically the ACPM fast path of sending
messages. If ACPM part is no-go then cpufreq is not needed.

Known TODO items:
 -- rx/tx channels locks rework;
 -- initial frequency fetching: Exynos850 firmware currently lacks a
    clean get_rate, so the driver falls back to dump defaults until the
    first freq transition.
 -- potential mailbox channels re-implementation.

Any thoughts, testing, or feedback on the architecture would be greatly
appreciated.

This was tested on Exynos850 with example of DT nodes described
in [1] and [2].

Dependencies are different series that adds Exynos850 ACPM support:
-- ACPM mailbox support for Exynos850:
https://lore.kernel.org/linux-samsung-soc/20260429-exynos...
-- sram DT node:
https://lore.kernel.org/linux-samsung-soc/20260413-exynos...
-- ACPM support on Exynos850: 
https://lore.kernel.org/linux-samsung-soc/20260513-exynos...

(the above dependencies pull some other series as well)

[1]:

cpu0: cpu@0 {
	device_type = "cpu";
	compatible = "arm,cortex-a55";
	reg = <0x0>;
	clocks = <&acpm_ipc E850_CLK_ACPM_DVFS_CPUCL0>;
	enable-method = "psci";
	operating-points-v2 = <&cpucl0_opp_table>;
	capacity-dmips-mhz = <250>;
	dynamic-power-coefficient = <70>;
};

[2]:

	cpucl0_opp_table: opp-table-0 {
		compatible = "operating-points-v2";
		opp-shared;

		opp-130000000 {
			opp-hz = /bits/ 64 <130000000>;
			opp-microvolt = <625000>;
			clock-latency-ns = <500000>;
		};

		opp-182000000 {
			opp-hz = /bits/ 64 <182000000>;
			opp-microvolt = <625000>;
			clock-latency-ns = <500000>;
		};

		opp-247000000 {
			opp-hz = /bits/ 64 <247000000>;
			opp-microvolt = <625000>;
			clock-latency-ns = <500000>;
		};

		opp-351000000 {
			opp-hz = /bits/ 64 <351000000>;
			opp-microvolt = <625000>;
			clock-latency-ns = <500000>;
		};

		opp-442000000 {
			opp-hz = /bits/ 64 <442000000>;
			opp-microvolt = <625000>;
			clock-latency-ns = <500000>;
		};

		opp-546000000 {
			opp-hz = /bits/ 64 <546000000>;
			opp-microvolt = <625000>;
			clock-latency-ns = <500000>;
		};

		opp-650000000 {
			opp-hz = /bits/ 64 <650000000>;
			opp-microvolt = <625000>;
			clock-latency-ns = <500000>;
		};

		opp-806000000 {
			opp-hz = /bits/ 64 <806000000>;
			opp-microvolt = <656250>;
			clock-latency-ns = <500000>;
		};

		opp-949000000 {
			opp-hz = /bits/ 64 <949000000>;
			opp-microvolt = <681250>;
			clock-latency-ns = <500000>;
		};

		opp-1053000000 {
			opp-hz = /bits/ 64 <1053000000>;
			opp-microvolt = <706250>;
			clock-latency-ns = <500000>;
		};

		opp-1157000000 {
			opp-hz = /bits/ 64 <1157000000>;
			opp-microvolt = <737500>;
			clock-latency-ns = <500000>;
		};

		opp-1300000000 {
			opp-hz = /bits/ 64 <1300000000>;
			opp-microvolt = <781250>;
			clock-latency-ns = <500000>;
		};

		opp-1456000000 {
			opp-hz = /bits/ 64 <1456000000>;
			opp-microvolt = <825000>;
			clock-latency-ns = <500000>;
		};

		opp-1586000000 {
			opp-hz = /bits/ 64 <1586000000>;
			opp-microvolt = <875000>;
			clock-latency-ns = <500000>;
		};

		opp-1742000000 {
			opp-hz = /bits/ 64 <1742000000>;
			opp-microvolt = <937500>;
			clock-latency-ns = <500000>;
		};

		opp-1846000000 {
			opp-hz = /bits/ 64 <1846000000>;
			opp-microvolt = <981250>;
			clock-latency-ns = <500000>;
		};

		opp-2002000000 {
			opp-hz = /bits/ 64 <2002000000>;
			opp-microvolt = <1050000>;
			clock-latency-ns = <500000>;
		};

		opp-2106000000 {
			opp-hz = /bits/ 64 <2106000000>;
			opp-microvolt = <1106250>;
			clock-latency-ns = <500000>;
		};

		opp-2210000000 {
			opp-hz = /bits/ 64 <2210000000>;
			opp-microvolt = <1181250>;
			clock-latency-ns = <500000>;
		};
	};

Signed-off-by: Alexey Klimov <alexey.klimov@linaro.org>
---
Alexey Klimov (2):
      firmware: samsung: acpm: add fire-and-forget xfer support
      cpufreq: add ACPM-based CPU DVFS driver for Exynos SoCs

 drivers/cpufreq/Kconfig.arm                        |   8 +
 drivers/cpufreq/Makefile                           |   1 +
 drivers/cpufreq/acpm-cpufreq.c                     | 195 +++++++++++++++++++++
 drivers/cpufreq/cpufreq-dt-platdev.c               |   3 +
 drivers/firmware/samsung/exynos-acpm-dvfs.c        |  14 ++
 drivers/firmware/samsung/exynos-acpm-dvfs.h        |   3 +
 drivers/firmware/samsung/exynos-acpm.c             | 142 +++++++++++++--
 drivers/firmware/samsung/exynos-acpm.h             |   3 +
 .../linux/firmware/samsung/exynos-acpm-protocol.h  |   2 +
 9 files changed, 361 insertions(+), 10 deletions(-)
---
base-commit: ec039126b7fac4e3af35ebccaa7c6f9b6875ba81
change-id: 20260612-acpm-fast-xfer-86c4de78c20b

Best regards,
-- 
Alexey Klimov <alexey.klimov@linaro.org>