cpufreq: Add SFI based cpufreq driver support

This adds the SFI based cpu freq driver for some of the Intel's Silvermont based Atom architectures like Z34xx and Z35xx.

---
v2:
(v2-v3: comments from Viresh)
* rephrase the Kconfig text
* merge the header file as its not being shared with anyone
* remove the unnecessary checks in sfi_cpufreq_target
* style changes in kzalloc
* fix the potential memory leak sfi_cpufreq_cpu_init
* move the cpufreq driver flag to the structure definition
* remove the redundant init of policy->cpu and policy->cur
* remove the unnecessary check while init the freq table
* merge the for loops in cpu_init
* use cpufreq_generic_attr rather than the custom one

v3:
* Add this change log
* remove the left over not used cached_freq var
* merge yet another for loop in cpu_init

v4:
* remove unnecessary pr_debug
* rephrase Kconfig text
* remove unused macro SFI_CPU_MAX
* Add Viresh's Acked-by

v5:
(comments from Len Brown)
* rename few private functions with sfi_cpufreq_ prefix
* move the PERF_CTL_MASK to msr-index.h
* make the driver.get current freq to refer PERF_CTRL
* remove sfi_processor_px, rather reuse sfi_freq_table_entry
* remove unnecessary memcpy, rather just point to the freq table
* consolidate get_performance_states with parse_freq
* remove extract_freq and make get_cur_freq to read from MSR directly
* move the state_count check while registering the perf states

v6:
* release the mutex in case of error in register_performance (comments from Viresh)
* drop local perf pointer in ->target and ->init
* fix the order of freeing memories in the error path of ->init
* remove alloc_percpu, rather allocate it at runtime in ->init

v7:
(comments from Len Brown)
* drop the unnecessary mutex
* move sfi_table_parse to __init as it is global to the system
* drop ->get callback
* consolidate few global data structures

v8:
(Viresh)
* drop per-cpu usage
(Len Brown)
* drop the usage of SFI_FREQ_MAX
* remove the logic of detecting transition_latency
* remove the last redundant pr_debug in ->init

v9:
(Len Brown)
* set up the freq table only once in __init and
point all cpus to it

 arch/x86/include/uapi/asm/msr-index.h |    1 +
 drivers/cpufreq/Kconfig.x86           |   10 +++
 drivers/cpufreq/Makefile              |    1 +
 drivers/cpufreq/sfi-cpufreq.c         |  136 +++++++++++++++++++++++++++++++++
 4 files changed, 148 insertions(+)
 create mode 100644 drivers/cpufreq/sfi-cpufreq.c

index c8aa65d56027..d11e1c57cfc5 100644
@@ -358,6 +358,7 @@
 
 #define MSR_IA32_PERF_STATUS		0x00000198
 #define MSR_IA32_PERF_CTL		0x00000199
+#define INTEL_PERF_CTL_MASK		0xffff
 #define MSR_AMD_PSTATE_DEF_BASE		0xc0010064
 #define MSR_AMD_PERF_STATUS		0xc0010063
 #define MSR_AMD_PERF_CTL		0xc0010062

index 89ae88f91895..c59bdcb83217 100644
@@ -57,6 +57,16 @@ config X86_ACPI_CPUFREQ_CPB
 	  By enabling this option the acpi_cpufreq driver provides the old
 	  entry in addition to the new boost ones, for compatibility reasons.
 
+config X86_SFI_CPUFREQ
+	tristate "SFI Performance-States driver"
+	depends on X86_INTEL_MID && SFI
+	help
+	  This adds a CPUFreq driver for some Silvermont based Intel Atom
+	  architectures like Z34xx and Z35xx which enumerate processor
+	  performance states through SFI.
+
+	  If in doubt, say N.
+
 config ELAN_CPUFREQ
 	tristate "AMD Elan SC400 and SC410"
 	depends on MELAN

index b3ca7b0b2c33..8b4220ac888b 100644
@@ -41,6 +41,7 @@ obj-$(CONFIG_X86_P4_CLOCKMOD)		+= p4-clockmod.o
 obj-$(CONFIG_X86_CPUFREQ_NFORCE2)	+= cpufreq-nforce2.o
 obj-$(CONFIG_X86_INTEL_PSTATE)		+= intel_pstate.o
 obj-$(CONFIG_X86_AMD_FREQ_SENSITIVITY)	+= amd_freq_sensitivity.o
+obj-$(CONFIG_X86_SFI_CPUFREQ)		+= sfi-cpufreq.o
 
 ##################################################################################
 # ARM SoC drivers

1.7.9.5

Good work!
Applied.

thanks,
Len Brown, Intel Open Source Technology Center