intel_pstate: provide option to only use intel_pstate with HWP

Allow users the option to disable the driver for any hardware
which does not support HWP.

Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

2 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4df73da11adc..07e6701a1439 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1469,6 +1469,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                        no_hwp
                          Do not enable hardware P state control (HWP)
                          if available.
+                hwp_only
+                        Only load intel_pstate on systems which support
+                        hardware P state control (HWP) if available.
 
         intremap=       [X86-64, Intel-IOMMU]
                         on      enable Interrupt Remapping (default)
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index e7e808d9a8af..872c5772c5d3 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1019,6 +1019,7 @@ static struct cpufreq_driver intel_pstate_driver = {
 
 static int __initdata no_load;
 static int __initdata no_hwp;
+static int __initdata hwp_only;
 static unsigned int force_load;
 
 static int intel_pstate_msrs_not_valid(void)
@@ -1216,6 +1217,9 @@ static int __init intel_pstate_init(void)
         if (cpu_has(c,X86_FEATURE_HWP) && !no_hwp)
                 intel_pstate_hwp_enable();
 
+        if (!hwp_active && hwp_only)
+                goto out;
+
         rc = cpufreq_register_driver(&intel_pstate_driver);
         if (rc)
                 goto out;
@@ -1250,6 +1254,8 @@ static int __init intel_pstate_setup(char *str)
                 no_hwp = 1;
         if (!strcmp(str, "force"))
                 force_load = 1;
+        if (!strcmp(str, "hwp_only"))
+                hwp_only = 1;
         return 0;
 }
 early_param("intel_pstate", intel_pstate_setup);