From: Penny Zheng <penny.zheng@amd.com>

amd-cppc on active mode bypasses the scaling governor layer, and
provides its own P-state selection algorithms in hardware. Consequently,
when it is used, the driver's -> setpolicy() callback is invoked
to register per-CPU utilization update callbacks, not the ->target()
callback.

So, only when cpufreq_driver.setpolicy is NULL, we need to deliberately
set old gov as NULL to trigger the according gov starting.

Signed-off-by: Penny Zheng <Penny.Zheng@amd.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
 xen/drivers/cpufreq/cpufreq.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/xen/drivers/cpufreq/cpufreq.c b/xen/drivers/cpufreq/cpufreq.c
index 792e4dc02c..8fc6e527c2 100644
--- a/xen/drivers/cpufreq/cpufreq.c
+++ b/xen/drivers/cpufreq/cpufreq.c
@@ -353,7 +353,13 @@ int cpufreq_add_cpu(unsigned int cpu)
     if (hw_all || (cpumask_weight(cpufreq_dom->map) ==
                    pmpt->domain_info.num_processors)) {
         memcpy(&new_policy, policy, sizeof(struct cpufreq_policy));
-        policy->governor = NULL;
+
+       /*
+        * Only when cpufreq_driver.setpolicy == NULL, we need to deliberately
+        * set old gov as NULL to trigger the according gov starting.
+        */
+       if ( cpufreq_driver.setpolicy == NULL )
+            policy->governor = NULL;
 
         cpufreq_cmdline_common_para(&new_policy);
 
-- 
2.34.1