[PATCH v6 4/6] x86/intel_pstate: add a booting param to select the driver to load

[Wei Wang <wei.w.wang@intel.com>]

By default, the old P-state driver (acpi-freq) is used. Adding
"intel_pstate" to the Xen booting param list to enable the
use of intel_pstate. However, if intel_pstate is enabled on a
machine which does not support the driver (e.g. Nehalem), the
old P-state driver will be loaded due to the failure loading of
intel_pstate.

Also, adding the intel_pstate booting parameter to
xen-command-line.markdown.

Signed-off-by: Wei Wang <wei.w.wang@intel.com>
---
 changes in v6:
 1) move the declaration of intel_pstate_init() to this patch.

 docs/misc/xen-command-line.markdown |  7 +++++++
 xen/arch/x86/acpi/cpufreq/cpufreq.c | 15 ++++++++++-----
 xen/include/asm-x86/cpufreq.h       |  2 ++
 3 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
index 416e559..e57a23a 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -858,6 +858,13 @@ debug hypervisor only).
 ### idle\_latency\_factor
 > `= <integer>`
 
+### intel\_pstate
+> `= <boolean>`
+
+> Default: `false`
+
+Enable the loading of the intel pstate driver.
+
 ### ioapic\_ack
 > `= old | new`
 
diff --git a/xen/arch/x86/acpi/cpufreq/cpufreq.c b/xen/arch/x86/acpi/cpufreq/cpufreq.c
index a2ba0db..d59f251 100644
--- a/xen/arch/x86/acpi/cpufreq/cpufreq.c
+++ b/xen/arch/x86/acpi/cpufreq/cpufreq.c
@@ -40,6 +40,7 @@
 #include <asm/processor.h>
 #include <asm/percpu.h>
 #include <asm/cpufeature.h>
+#include <asm/cpufreq.h>
 #include <acpi/acpi.h>
 #include <acpi/cpufreq/cpufreq.h>
 
@@ -647,11 +648,15 @@ static int __init cpufreq_driver_init(void)
 {
     int ret = 0;
 
-    if ((cpufreq_controller == FREQCTL_xen) &&
-        (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL))
-        ret = cpufreq_register_driver(&acpi_cpufreq_driver);
-    else if ((cpufreq_controller == FREQCTL_xen) &&
-        (boot_cpu_data.x86_vendor == X86_VENDOR_AMD))
+    if ( (cpufreq_controller == FREQCTL_xen) &&
+         (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) )
+    {
+        ret = intel_pstate_init();
+        if ( ret )
+            ret = cpufreq_register_driver(&acpi_cpufreq_driver);
+    }
+    else if ( (cpufreq_controller == FREQCTL_xen) &&
+              (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) )
         ret = powernow_register_driver();
 
     return ret;
diff --git a/xen/include/asm-x86/cpufreq.h b/xen/include/asm-x86/cpufreq.h
index afc72df..3ff516d 100644
--- a/xen/include/asm-x86/cpufreq.h
+++ b/xen/include/asm-x86/cpufreq.h
@@ -22,6 +22,8 @@
  * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  */
 
+extern int intel_pstate_init(void);
+
 /*
  * Maximum transition latency is in nanoseconds - if it's unknown,
  * CPUFREQ_ETERNAL shall be used.
-- 
1.9.1