[PATCH v10 13/15] iommu/arm-smmu-v3: Enable pm_runtime and setup devlinks

[Pranjal Shrivastava <praan@google.com>]

Enable PM runtime for SMMUs having a power-domain during smmu probe.
Add a devlink between the clients and SMMU device. The absence of a
power domain effectively disables runtime power management.

Additionally, handle runtime PM teardown in arm_smmu_disable_action()
and skip MMIO accesses during teardown and shutdown if the SMMU is
already runtime suspended, as translation is already disabled and the
hardware is in a low-power state.

Reviewed-by: Mostafa Saleh <smostafa@google.com>
Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 49 +++++++++++++++++++--
 1 file changed, 46 insertions(+), 3 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 1c5d891564e4..0a83d495d8d2 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -4511,8 +4511,28 @@ static struct iommu_device *arm_smmu_probe_device(struct device *dev)
 	if (ret)
 		goto err_disable_pasid;
 
+	/*
+	 * If linking fails on an RPM-enabled SMMU, abort probe to prevent
+	 * DMA transactions while the SMMU is autosuspended. Otherwise, warn
+	 * and continue since the SMMU is always powered.
+	 */
+	if (!device_link_add(dev, smmu->dev,
+			     DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_SUPPLIER)) {
+		if (pm_runtime_enabled(smmu->dev)) {
+			dev_err(smmu->dev, "failed to add devlink to %s\n",
+				dev_name(dev));
+			ret = -ENOMEM;
+			goto err_free_cd_tables;
+		}
+
+		dev_warn(smmu->dev, "failed to add devlink to %s\n", dev_name(dev));
+	}
+
 	return &smmu->iommu;
 
+err_free_cd_tables:
+	if (arm_smmu_cdtab_allocated(&master->cd_table))
+		arm_smmu_free_cd_tables(master);
 err_disable_pasid:
 	arm_smmu_disable_pasid(master);
 	arm_smmu_remove_master(master);
@@ -5116,9 +5136,17 @@ static void arm_smmu_disable_action(void *data)
 {
 	struct arm_smmu_device *smmu = data;
 
-	if (smmu->impl_ops && smmu->impl_ops->device_disable)
-		smmu->impl_ops->device_disable(smmu);
-	arm_smmu_device_disable(smmu);
+	/* If the SMMU is already suspended, nothing to do */
+	if (!pm_runtime_suspended(smmu->dev)) {
+		if (smmu->impl_ops && smmu->impl_ops->device_disable)
+			smmu->impl_ops->device_disable(smmu);
+		arm_smmu_device_disable(smmu);
+	}
+
+	if (pm_runtime_enabled(smmu->dev)) {
+		pm_runtime_dont_use_autosuspend(smmu->dev);
+		pm_runtime_disable(smmu->dev);
+	}
 }
 
 static void arm_smmu_write_strtab(struct arm_smmu_device *smmu)
@@ -5931,6 +5959,17 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
 		return ret;
 	}
 
+	/*
+	 * Safe to enable RPM here as client devices cannot be probed
+	 * before this probe function successfully returns.
+	 */
+	if (dev->pm_domain) {
+		pm_runtime_set_active(dev);
+		pm_runtime_use_autosuspend(dev);
+		pm_runtime_set_autosuspend_delay(dev, RPM_AUTOSUSPEND_DELAY_MS);
+		pm_runtime_enable(dev);
+	}
+
 	return 0;
 }
 
@@ -5946,6 +5985,10 @@ static void arm_smmu_device_shutdown(struct platform_device *pdev)
 {
 	struct arm_smmu_device *smmu = platform_get_drvdata(pdev);
 
+	/* If the SMMU is already suspended, nothing to do */
+	if (pm_runtime_suspended(&pdev->dev))
+		return;
+
 	arm_smmu_device_disable(smmu);
 }
 
-- 
2.55.0.979.g7e5102b832-goog