[PATCHv3 2/2] nvme-pci: Use host managed power state for suspend

[keith.busch@intel.com (Keith Busch)]

The nvme pci driver prepares its devices for power loss during suspend
by shutting down the controllers. The power setting is deferred to
pci driver's power management before the platform removes power. The
suspend-to-idle mode, however, does not remove power.

NVMe devices that implement host managed power settings can achieve
lower power and better transition latencies than using generic PCI power
settings. Try to use this feature if the platform is not involved with
the suspend. If successful, restore the previous power state on resume.

Cc: Mario Limonciello <Mario.Limonciello at dell.com>
Cc: Kai Heng Feng <kai.heng.feng at canonical.com>
Signed-off-by: Keith Busch <keith.busch at intel.com>
---
v2 -> v3:

  Removed the HMB handling. We've determined this is not be
  necessary in a s2i state.

  Splitting PM ops (Rafael)

  Incorporated improvements from Christoph

 drivers/nvme/host/pci.c | 96 +++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 93 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 599065ed6a32..47da55abb56b 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -18,6 +18,7 @@
 #include <linux/mutex.h>
 #include <linux/once.h>
 #include <linux/pci.h>
+#include <linux/suspend.h>
 #include <linux/t10-pi.h>
 #include <linux/types.h>
 #include <linux/io-64-nonatomic-lo-hi.h>
@@ -116,6 +117,7 @@ struct nvme_dev {
 	u32 cmbsz;
 	u32 cmbloc;
 	struct nvme_ctrl ctrl;
+	u32 last_ps;
 
 	mempool_t *iod_mempool;
 
@@ -2829,16 +2831,94 @@ static void nvme_remove(struct pci_dev *pdev)
 }
 
 #ifdef CONFIG_PM_SLEEP
+static int nvme_get_power_state(struct nvme_ctrl *ctrl, u32 *ps)
+{
+	return nvme_get_features(ctrl, NVME_FEAT_POWER_MGMT, 0, NULL, 0, ps);
+}
+
+static int nvme_set_power_state(struct nvme_ctrl *ctrl, u32 ps)
+{
+	return nvme_set_features(ctrl, NVME_FEAT_POWER_MGMT, ps, NULL, 0, NULL);
+}
+
+static int nvme_resume(struct device *dev)
+{
+	struct nvme_dev *ndev = pci_get_drvdata(to_pci_dev(dev));
+	struct nvme_ctrl *ctrl = &ndev->ctrl;
+
+	if (pm_resume_via_firmware() || !ctrl->npss ||
+	    nvme_set_power_state(ctrl, ndev->last_ps) != 0)
+		nvme_reset_ctrl(ctrl);
+	return 0;
+}
+
 static int nvme_suspend(struct device *dev)
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
 	struct nvme_dev *ndev = pci_get_drvdata(pdev);
+	struct nvme_ctrl *ctrl = &ndev->ctrl;
+	int ret = -EBUSY;
+
+	/*
+	 * The platform does not remove power for a kernel managed suspend so
+	 * use host managed nvme power settings for lowest idle power if
+	 * possible. This should have quicker resume latency than a full device
+	 * shutdown.  But if the firmware is involved after the suspend or the
+	 * device does not support any non-default power states, shut down the
+	 * device fully.
+	 */
+	if (pm_suspend_via_firmware() || !ctrl->npss) {
+		nvme_dev_disable(ndev, true);
+		return 0;
+	}
+
+	nvme_start_freeze(ctrl);
+	nvme_wait_freeze(ctrl);
+	nvme_sync_queues(ctrl);
+
+	if (ctrl->state != NVME_CTRL_LIVE &&
+	    ctrl->state != NVME_CTRL_ADMIN_ONLY)
+		goto unfreeze;
+
+	ndev->last_ps = 0;
+	ret = nvme_get_power_state(ctrl, &ndev->last_ps);
+	if (ret < 0)
+		goto unfreeze;
+
+	ret = nvme_set_power_state(ctrl, ctrl->npss);
+	if (ret < 0)
+		goto unfreeze;
+
+	if (ret) {
+		/*
+		 * Clearing npss forces a controller reset on resume. The
+		 * correct value will be resdicovered then.
+		 */
+		nvme_dev_disable(ndev, true);
+		ctrl->npss = 0;
+		ret = 0;
+		goto unfreeze;
+	}
+	/*
+	 * A saved state prevents pci pm from generically controlling the
+	 * device's power. If we're using protocol specific settings, we don't
+	 * want pci interfering.
+	 */
+	pci_save_state(pdev);
+unfreeze:
+	nvme_unfreeze(ctrl);
+	return ret;
+}
+
+static int nvme_simple_suspend(struct device *dev)
+{
+	struct nvme_dev *ndev = pci_get_drvdata(to_pci_dev(dev));
 
 	nvme_dev_disable(ndev, true);
 	return 0;
 }
 
-static int nvme_resume(struct device *dev)
+static int nvme_simple_resume(struct device *dev)
 {
 	struct pci_dev *pdev = to_pci_dev(dev);
 	struct nvme_dev *ndev = pci_get_drvdata(pdev);
@@ -2846,9 +2926,19 @@ static int nvme_resume(struct device *dev)
 	nvme_reset_ctrl(&ndev->ctrl);
 	return 0;
 }
-#endif
 
-static SIMPLE_DEV_PM_OPS(nvme_dev_pm_ops, nvme_suspend, nvme_resume);
+const struct dev_pm_ops nvme_dev_pm_ops = {
+	.suspend	= nvme_suspend,
+	.resume		= nvme_resume,
+	.freeze		= nvme_simple_suspend,
+	.thaw		= nvme_simple_resume,
+	.poweroff	= nvme_simple_suspend,
+	.restore	= nvme_simple_resume,
+};
+
+#else
+#define nvme_dev_pm_ops		NULL
+#endif
 
 static pci_ers_result_t nvme_error_detected(struct pci_dev *pdev,
 						pci_channel_state_t state)
-- 
2.14.4