[PATCH 2/6] cpufreq: amd-pstate: cpufreq: amd-pstate: reset MSR_AMD_PERF_CTL register at init

[Paolo Pisati]

From: Wyes Karny <wyes.karny at amd.com>

BugLink: https://bugs.launchpad.net/bugs/1998106

MSR_AMD_PERF_CTL is guaranteed to be 0 on a cold boot. However, on a
kexec boot, for instance, it may have a non-zero value (if the cpu was
in a non-P0 Pstate).  In such cases, the cores with non-P0 Pstates at
boot will never be pushed to P0, let alone boost frequencies.

Kexec is a common workflow for reboot on Linux and this creates a
regression in performance. Fix it by explicitly setting the
MSR_AMD_PERF_CTL to 0 during amd_pstate driver init.

Cc: All applicable <stable at vger.kernel.org>
Acked-by: Huang Rui <ray.huang at amd.com>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy at amd.com>
Tested-by: Wyes Karny <wyes.karny at amd.com>
Signed-off-by: Wyes Karny <wyes.karny at amd.com>
Signed-off-by: Perry Yuan <Perry.Yuan at amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
(cherry picked from commit 919f4557696939625085435ebde09a539de2349c)
Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
---
 drivers/cpufreq/amd-pstate.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index d63a28c5f95a..3147a53bd3a6 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -483,12 +483,22 @@ static void amd_pstate_boost_init(struct amd_cpudata *cpudata)
 	amd_pstate_driver.boost_enabled = true;
 }
 
+static void amd_perf_ctl_reset(unsigned int cpu)
+{
+	wrmsrl_on_cpu(cpu, MSR_AMD_PERF_CTL, 0);
+}
+
 static int amd_pstate_cpu_init(struct cpufreq_policy *policy)
 {
 	int min_freq, max_freq, nominal_freq, lowest_nonlinear_freq, ret;
 	struct device *dev;
 	struct amd_cpudata *cpudata;
 
+	/*
+	 * Resetting PERF_CTL_MSR will put the CPU in P0 frequency,
+	 * which is ideal for initialization process.
+	 */
+	amd_perf_ctl_reset(policy->cpu);
 	dev = get_cpu_device(policy->cpu);
 	if (!dev)
 		return -ENODEV;
-- 
2.34.1