cpufreq: amd-pstate: cpufreq: amd-pstate: reset MSR_AMD_PERF_CTL register at init

Bugzilla: https://bugzilla.redhat.com/2150425

commit 919f455
Author: Wyes Karny <wyes.karny@amd.com>
Date:   Thu Nov 17 15:35:37 2022 +0800

    cpufreq: amd-pstate: cpufreq: amd-pstate: reset MSR_AMD_PERF_CTL register at init

    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@vger.kernel.org>
    Acked-by: Huang Rui <ray.huang@amd.com>
    Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
    Tested-by: Wyes Karny <wyes.karny@amd.com>
    Signed-off-by: Wyes Karny <wyes.karny@amd.com>
    Signed-off-by: Perry Yuan <Perry.Yuan@amd.com>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Signed-off-by: David Arcari <darcari@redhat.com>

Author: darcari

drivers/cpufreq/amd-pstate.c

@@ -424,12 +424,22 @@ 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;