cpufreq: mediatek: allow building as a module

The MT8173 cpufreq driver can currently only be built-in, but
it has a Kconfig dependency on the thermal core. THERMAL
can be a loadable module, which in turn makes this driver
impossible to build.

It is nicer to make the cpufreq driver a module as well, so
this patch turns the option in to a 'tristate' and adapts
the dependency accordingly.

The driver has no module_exit() function, so it will continue
to not support unloading, but it can be built as a module
and loaded at runtime now.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 5269e7067cd6 (cpufreq: Add ARM_MT8173_CPUFREQ dependency on THERMAL)
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/Kconfig.arm

@@ -84,10 +84,10 @@ config ARM_KIRKWOOD_CPUFREQ
 	  SoCs.
 
 config ARM_MT8173_CPUFREQ
-	bool "Mediatek MT8173 CPUFreq support"
+	tristate "Mediatek MT8173 CPUFreq support"
 	depends on ARCH_MEDIATEK && REGULATOR
 	depends on ARM64 || (ARM_CPU_TOPOLOGY && COMPILE_TEST)
-	depends on !CPU_THERMAL || THERMAL=y
+	depends on !CPU_THERMAL || THERMAL
 	select PM_OPP
 	help
 	  This adds the CPUFreq driver support for Mediatek MT8173 SoC.

drivers/cpufreq/mt8173-cpufreq.c

@@ -17,6 +17,7 @@
 #include <linux/cpu_cooling.h>
 #include <linux/cpufreq.h>
 #include <linux/cpumask.h>
+#include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/pm_opp.h>