linux-kernel - [PATCH V3 2/2] platform/x86/intel/pmc: Disable C1 auto-demotion during suspend

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Message-ID: <20241017210439.3449324-2-david.e.box@linux.intel.com>
Date: Thu, 17 Oct 2024 14:04:38 -0700
From: "David E. Box" <david.e.box@...ux.intel.com>
To: david.e.box@...el.com,
	hdegoede@...hat.com,
	ilpo.jarvinen@...ux.intel.com,
	platform-driver-x86@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org,
	rjw@...ysocki.net,
	srinivas.pandruvada@...ux.intel.com,
	ricardo.neri-calderon@...ux.intel.com
Subject: [PATCH V3 2/2] platform/x86/intel/pmc: Disable C1 auto-demotion during suspend

On some platforms, aggressive C1 auto-demotion may lead to failure to enter
the deepest C-state during suspend-to-idle, causing high power consumption.
To prevent this, disable C1 auto-demotion during suspend and re-enable on
resume.

Signed-off-by: David E. Box <david.e.box@...ux.intel.com>
---
V3 - Use s2idle wrapper function suggested by Rafael
   - Use on_each_cpu() suggested by Ricardo

V2 - Remove #define DEBUG
   - Move refactor of cnl_resume() to separate patch
   - Use smp_call_function() to disable and restore C1_AUTO_DEMOTE
   - Add comment that the MSR is per core, not per package.
   - Add comment that the online cpu mask remains unchanged during
     suspend due to frozen userspace.

 drivers/platform/x86/intel/pmc/cnp.c | 53 ++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/drivers/platform/x86/intel/pmc/cnp.c b/drivers/platform/x86/intel/pmc/cnp.c
index 513c02670c5a..3eaad2a7ebf4 100644
--- a/drivers/platform/x86/intel/pmc/cnp.c
+++ b/drivers/platform/x86/intel/pmc/cnp.c
@@ -8,6 +8,8 @@
  *
  */
 
+#include <linux/smp.h>
+#include <linux/suspend.h>
 #include "core.h"
 
 /* Cannon Lake: PGD PFET Enable Ack Status Register(s) bitmap */
@@ -206,8 +208,57 @@ const struct pmc_reg_map cnp_reg_map = {
 	.etr3_offset = ETR3_OFFSET,
 };
 
+
+/*
+ * Disable C1 auto-demotion
+ *
+ * Aggressive C1 auto-demotion may lead to failure to enter the deepest C-state
+ * during suspend-to-idle, causing high power consumption. To prevent this, we
+ * disable C1 auto-demotion during suspend and re-enable on resume.
+ *
+ * Note that, although MSR_PKG_CST_CONFIG_CONTROL has 'package' in its name, it
+ * is actually a per-core MSR on client platforms, affecting only a single CPU.
+ * Therefore, it must be configured on all online CPUs. The online cpu mask is
+ * unchanged during the phase of suspend/resume as user space is frozen.
+ */
+
+static DEFINE_PER_CPU(u64, pkg_cst_config);
+
+static void disable_c1_auto_demote(void *unused)
+{
+	int cpunum = smp_processor_id();
+	u64 val;
+
+	rdmsrl(MSR_PKG_CST_CONFIG_CONTROL, val);
+	per_cpu(pkg_cst_config, cpunum) = val;
+	val &= ~NHM_C1_AUTO_DEMOTE;
+	wrmsrl(MSR_PKG_CST_CONFIG_CONTROL, val);
+
+	pr_debug("%s: cpu:%d cst %llx\n", __func__, cpunum, val);
+}
+
+static void restore_c1_auto_demote(void *unused)
+{
+	int cpunum = smp_processor_id();
+
+	wrmsrl(MSR_PKG_CST_CONFIG_CONTROL, per_cpu(pkg_cst_config, cpunum));
+
+	pr_debug("%s: cpu:%d cst %llx\n", __func__, cpunum,
+		 per_cpu(pkg_cst_config, cpunum));
+}
+
+static void s2idle_cpu_quirk(smp_call_func_t func)
+{
+	if (pm_suspend_via_firmware())
+		return;
+
+	on_each_cpu(func, NULL, true);
+}
+
 void cnl_suspend(struct pmc_dev *pmcdev)
 {
+	s2idle_cpu_quirk(disable_c1_auto_demote);
+
 	/*
 	 * Due to a hardware limitation, the GBE LTR blocks PC10
 	 * when a cable is attached. To unblock PC10 during suspend,
@@ -218,6 +269,8 @@ void cnl_suspend(struct pmc_dev *pmcdev)
 
 int cnl_resume(struct pmc_dev *pmcdev)
 {
+	s2idle_cpu_quirk(restore_c1_auto_demote);
+
 	pmc_core_send_ltr_ignore(pmcdev, 3, 0);
 
 	return pmc_core_resume_common(pmcdev);
-- 
2.43.0