power: avs: Add support for CPR (Core Power Reduction)

CPR (Core Power Reduction) is a technology that reduces core power on a
CPU or other device. It reads voltage settings in efuse from product
test process as initial settings.
Each OPP corresponds to a "corner" that has a range of valid voltages
for a particular frequency. While the device is running at a particular
frequency, CPR monitors dynamic factors such as temperature, etc. and
adjusts the voltage for that frequency accordingly to save power
and meet silicon characteristic requirements.

This driver is based on an RFC by Stephen Boyd[1], which in turn is
based on work by others on codeaurora.org[2].

[1] https://lkml.org/lkml/2015/9/18/833
[2] https://source.codeaurora.org/quic/la/kernel/msm-4.14/tree/drivers/regulator/cpr-regulator.c?h=msm-4.14

Co-developed-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Niklas Cassel <niklas.cassel@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

MAINTAINERS

@@ -13667,6 +13667,14 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/opp/qcom-nvmem-cpufreq.txt
 F:	drivers/cpufreq/qcom-cpufreq-nvmem.c
 
+QUALCOMM CORE POWER REDUCTION (CPR) AVS DRIVER
+M:	Niklas Cassel <nks@flawful.org>
+L:	linux-pm@vger.kernel.org
+L:	linux-arm-msm@vger.kernel.org
+S:	Maintained
+F:	Documentation/devicetree/bindings/power/avs/qcom,cpr.txt
+F:	drivers/power/avs/qcom-cpr.c
+
 QUALCOMM EMAC GIGABIT ETHERNET DRIVER
 M:	Timur Tabi <timur@kernel.org>
 L:	netdev@vger.kernel.org

drivers/power/avs/Kconfig

@@ -12,6 +12,21 @@ menuconfig POWER_AVS
 
 	  Say Y here to enable Adaptive Voltage Scaling class support.
 
+config QCOM_CPR
+	tristate "QCOM Core Power Reduction (CPR) support"
+	depends on POWER_AVS
+	select PM_OPP
+	help
+	  Say Y here to enable support for the CPR hardware found on Qualcomm
+	  SoCs like QCS404.
+
+	  This driver populates CPU OPPs tables and makes adjustments to the
+	  tables based on feedback from the CPR hardware. If you want to do
+	  CPUfrequency scaling say Y here.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called qcom-cpr
+
 config ROCKCHIP_IODOMAIN
 	tristate "Rockchip IO domain support"
 	depends on POWER_AVS && ARCH_ROCKCHIP && OF

drivers/power/avs/Makefile

@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
 obj-$(CONFIG_POWER_AVS_OMAP)		+= smartreflex.o
+obj-$(CONFIG_QCOM_CPR)			+= qcom-cpr.o
 obj-$(CONFIG_ROCKCHIP_IODOMAIN)		+= rockchip-io-domain.o