cpufreq / intel_pstate: Add kernel command line option disable intel_pstate.

When intel_pstate is configured into the kernel it will become the
preferred scaling driver for processors that it supports.  Allow the
user to override this by adding:
   intel_pstate=disable
on the kernel command line.

Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

2 files changed, 21 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 363e348bff9b..b335c456feb9 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1131,6 +1131,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         0       disables intel_idle and fall back on acpi_idle.
                         1 to 6  specify maximum depth of C-state.
 
+        intel_pstate=  [X86]
+                       disable
+                         Do not enable intel_pstate as the default
+                         scaling driver for the supported processors
+
         intremap=       [X86-64, Intel-IOMMU]
                         on      enable Interrupt Remapping (default)
                         off     disable Interrupt Remapping
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index e87996355da0..096fde0ebcb5 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -773,11 +773,16 @@ static void intel_pstate_exit(void)
 }
 module_exit(intel_pstate_exit);
 
+static int __initdata no_load;
+
 static int __init intel_pstate_init(void)
 {
         int rc = 0;
         const struct x86_cpu_id *id;
 
+        if (no_load)
+                return -ENODEV;
+
         id = x86_match_cpu(intel_pstate_cpu_ids);
         if (!id)
                 return -ENODEV;
@@ -802,6 +807,17 @@ out:
 }
 device_initcall(intel_pstate_init);
 
+static int __init intel_pstate_setup(char *str)
+{
+        if (!str)
+                return -EINVAL;
+
+        if (!strcmp(str, "disable"))
+                no_load = 1;
+        return 0;
+}
+early_param("intel_pstate", intel_pstate_setup);
+
 MODULE_AUTHOR("Dirk Brandewie <dirk.j.brandewie@intel.com>");
 MODULE_DESCRIPTION("'intel_pstate' - P state driver Intel Core processors");
 MODULE_LICENSE("GPL");