cpufreq: Add Loongson-3 CPUFreq driver support

Some of LoongArch processors (Loongson-3 series) support DVFS, their
IOCSR.FEATURES has IOCSRF_FREQSCALE set. And they has a micro-core in
the package called SMC (System Management Controller), which can be
used to detect temperature, control fans, scale frequency and voltage,
etc.

The Loongson-3 CPUFreq driver is very simple now, it communicate with
SMC, get DVFS info, set target frequency from CPUFreq core, and so on.

There is a command list to interact with SMC, widely-used commands in
the CPUFreq driver include:

CMD_GET_VERSION: Get SMC firmware version.

CMD_GET_FEATURE: Get enabled SMC features.

CMD_SET_FEATURE: Enable SMC features, such as basic DVFS, BOOST.

CMD_GET_FREQ_LEVEL_NUM: Get the number of all frequency levels.

CMD_GET_FREQ_BOOST_LEVEL: Get the first boost frequency level.

CMD_GET_FREQ_LEVEL_INFO: Get the detail info of a frequency level.

CMD_GET_FREQ_INFO: Get the current frequency.

CMD_SET_FREQ_INFO: Set the target frequency.

In future we will add automatic frequency scaling, which is similar to
Intel's HWP (HardWare P-State).

Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
[ Viresh: Minor formatting cleanups, change return type of exit() to
	  void and use devm_mutex_init() ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

Author: chenhuacai

MAINTAINERS

@@ -12969,6 +12969,7 @@ F:	Documentation/arch/loongarch/
 F:	Documentation/translations/zh_CN/arch/loongarch/
 F:	arch/loongarch/
 F:	drivers/*/*loongarch*
+F:	drivers/cpufreq/loongson3_cpufreq.c
 
 LOONGSON GPIO DRIVER
 M:	Yinbo Zhu <zhuyinbo@loongson.cn>

drivers/cpufreq/Kconfig

@@ -262,6 +262,18 @@ config LOONGSON2_CPUFREQ
 	  If in doubt, say N.
 endif
 
+if LOONGARCH
+config LOONGSON3_CPUFREQ
+	tristate "Loongson3 CPUFreq Driver"
+	help
+	  This option adds a CPUFreq driver for Loongson processors which
+	  support software configurable cpu frequency.
+
+	  Loongson-3 family processors support this feature.
+
+	  If in doubt, say N.
+endif
+
 if SPARC64
 config SPARC_US3_CPUFREQ
 	tristate "UltraSPARC-III CPU Frequency driver"

drivers/cpufreq/Makefile

@@ -103,6 +103,7 @@ obj-$(CONFIG_POWERNV_CPUFREQ)		+= powernv-cpufreq.o
 # Other platform drivers
 obj-$(CONFIG_BMIPS_CPUFREQ)		+= bmips-cpufreq.o
 obj-$(CONFIG_LOONGSON2_CPUFREQ)		+= loongson2_cpufreq.o
+obj-$(CONFIG_LOONGSON3_CPUFREQ)		+= loongson3_cpufreq.o
 obj-$(CONFIG_SH_CPU_FREQ)		+= sh-cpufreq.o
 obj-$(CONFIG_SPARC_US2E_CPUFREQ)	+= sparc-us2e-cpufreq.o
 obj-$(CONFIG_SPARC_US3_CPUFREQ)		+= sparc-us3-cpufreq.o