[PATCH 2/2] nvme-pci: disable hmb on idle suspend

[Keith Busch]

An idle suspend may or may not disable host memory access from devices
placed in low power mode. Either way, it should always be safe to
disable the host memory buffer prior to entering the low power mode, and
this should also always be faster than a full device shutdown.

Cc: Kai-Heng Feng <kai.heng.feng at canonical.com>
Signed-off-by: Keith Busch <kbusch at kernel.org>
---
 drivers/nvme/host/pci.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index e8f3b32131d2..42d4cbe31a28 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -3130,8 +3130,13 @@ static int nvme_resume(struct device *dev)
 
 	if (ndev->last_ps == U32_MAX ||
 	    nvme_set_power_state(ctrl, ndev->last_ps) != 0)
-		return nvme_try_sched_reset(&ndev->ctrl);
+		goto reset;
+	if (ctrl->hmpre && nvme_setup_host_mem(ndev))
+		goto reset;
+
 	return 0;
+reset:
+	return nvme_try_sched_reset(ctrl);
 }
 
 static int nvme_suspend(struct device *dev)
@@ -3155,15 +3160,9 @@ static int nvme_suspend(struct device *dev)
 	 * the PCI bus layer to put it into D3 in order to take the PCIe link
 	 * down, so as to allow the platform to achieve its minimum low-power
 	 * state (which may not be possible if the link is up).
-	 *
-	 * If a host memory buffer is enabled, shut down the device as the NVMe
-	 * specification allows the device to access the host memory buffer in
-	 * host DRAM from all power states, but hosts will fail access to DRAM
-	 * during S3.
 	 */
 	if (pm_suspend_via_firmware() || !ctrl->npss ||
 	    !pcie_aspm_enabled(pdev) ||
-	    ndev->nr_host_mem_descs ||
 	    (ndev->ctrl.quirks & NVME_QUIRK_SIMPLE_SUSPEND))
 		return nvme_disable_prepare_reset(ndev, true);
 
@@ -3174,6 +3173,17 @@ static int nvme_suspend(struct device *dev)
 	if (ctrl->state != NVME_CTRL_LIVE)
 		goto unfreeze;
 
+	/*
+	 * Host memory access may not be successful in a system suspend state,
+	 * but the specification allows the controller to access memory in a
+	 * non-operational power state.
+	 */
+	if (ndev->hmb) {
+		ret = nvme_set_host_mem(ndev, 0);
+		if (ret < 0)
+			goto unfreeze;
+	}
+
 	ret = nvme_get_power_state(ctrl, &ndev->last_ps);
 	if (ret < 0)
 		goto unfreeze;
-- 
2.25.4