PM / devfreq: Add HiSilicon uncore frequency scaling driver

Add the HiSilicon uncore frequency scaling driver for Kunpeng SoCs based on
the devfreq framework.  The uncore domain contains shared computing
resources, including system interconnects and L3 cache.  The uncore
frequency significantly impacts the system-wide performance as well as
power consumption.  This driver adds support for runtime management of
uncore frequency from kernel and userspace.  The main function includes
setting and getting frequencies, changing frequency scaling policies, and
querying the list of CPUs whose performance is significantly related to
this uncore frequency domain, etc.  The driver communicates with a platform
controller through an ACPI PCC mailbox to take the actual actions of
frequency scaling.

Co-developed-by: Lifeng Zheng <zhenglifeng1@huawei.com>
Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Huisong Li <lihuisong@huawei.com>
Signed-off-by: Jie Zhan <zhanjie9@hisilicon.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Link: https://patchwork.kernel.org/project/linux-pm/patch/20250623143401.4095045-3-zhanjie9@hisilicon.com/

Documentation/ABI/testing/sysfs-class-devfreq

@@ -132,3 +132,12 @@ Description:
 
 		A list of governors that support the node:
 		- simple_ondemand
+
+What:		/sys/class/devfreq/.../related_cpus
+Date:		June 2025
+Contact:	Linux power management list <linux-pm@vger.kernel.org>
+Description:	The list of CPUs whose performance is closely related to the
+		frequency of this devfreq domain.
+
+		This file is only present if a specific devfreq device is
+		closely associated with a subset of CPUs.

drivers/devfreq/Kconfig

@@ -90,6 +90,17 @@ config ARM_EXYNOS_BUS_DEVFREQ
 	  and adjusts the operating frequencies and voltages with OPP support.
 	  This does not yet operate with optimal voltages.
 
+config ARM_HISI_UNCORE_DEVFREQ
+	tristate "HiSilicon uncore DEVFREQ Driver"
+	depends on ACPI && ACPI_PPTT && PCC
+	select DEVFREQ_GOV_PERFORMANCE
+	select DEVFREQ_GOV_USERSPACE
+	help
+	  This adds a DEVFREQ driver that manages uncore frequency scaling for
+	  HiSilicon Kunpeng SoCs. This enables runtime management of uncore
+	  frequency scaling from kernel and userspace. The uncore domain
+	  contains system interconnects and L3 cache.
+
 config ARM_IMX_BUS_DEVFREQ
 	tristate "i.MX Generic Bus DEVFREQ Driver"
 	depends on ARCH_MXC || COMPILE_TEST

drivers/devfreq/Makefile

@@ -9,6 +9,7 @@ obj-$(CONFIG_DEVFREQ_GOV_PASSIVE)	+= governor_passive.o
 
 # DEVFREQ Drivers
 obj-$(CONFIG_ARM_EXYNOS_BUS_DEVFREQ)	+= exynos-bus.o
+obj-$(CONFIG_ARM_HISI_UNCORE_DEVFREQ)	+= hisi_uncore_freq.o
 obj-$(CONFIG_ARM_IMX_BUS_DEVFREQ)	+= imx-bus.o
 obj-$(CONFIG_ARM_IMX8M_DDRC_DEVFREQ)	+= imx8m-ddrc.o
 obj-$(CONFIG_ARM_MEDIATEK_CCI_DEVFREQ)	+= mtk-cci-devfreq.o