Re: [PATCH v11 13/16] iommu/arm-smmu-v3: Implement pm_runtime & system sleep ops

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
index 0a841441cc44..d0a3d497915c 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h

@@ -663,11 +663,14 @@ arm_smmu_make_cmd_tlbi(enum arm_smmu_cmdq_opcode op, u16 asid, u16 vmid)

+#define RPM_AUTOSUSPEND_DELAY_MS	15
+
 struct arm_smmu_ll_queue {
 	union {
 		u64			val;

@@ -1234,6 +1237,18 @@ int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu,
 				bool sync);
 bool arm_smmu_erratum_repeat_tlbi_cfgi(void);
 
+/*
+ * Lockless pre-check to test if the SMMU is actively powered.
+ * Races with concurrent suspend are benign: the cmpxchg loop in
+ * arm_smmu_cmdq_issue_cmdlist() acts as the true commit point.
+ * If we lose the race, that loop observes Q_STOP == 1 and safely
+ * drops the command. If we win, the suspend thread waits for us.
+ */
+static inline bool arm_smmu_is_active(struct arm_smmu_device *smmu)
+{
+	return !Q_STOP(READ_ONCE(smmu->cmdq.q.llq.prod));
+}

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 89a4e756ff17..e127e3be3a6b 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

@@ -29,6 +29,7 @@
 #include <linux/platform_device.h>
 #include <linux/sort.h>
 #include <linux/string_choices.h>
+#include <linux/pm_runtime.h>
 #include <kunit/visibility.h>
 #include <uapi/linux/iommufd.h>
 

@@ -119,6 +120,45 @@ static const char * const event_class_str[] = {
 static int arm_smmu_alloc_cd_tables(struct arm_smmu_master *master);
 static bool arm_smmu_ats_supported(struct arm_smmu_master *master);
 
+/* Runtime PM helpers */
+__maybe_unused static int arm_smmu_rpm_get(struct arm_smmu_device *smmu)
+{
+	int ret;
+
+	if (!pm_runtime_enabled(smmu->dev))
+		return 0;
+
+	ret = pm_runtime_resume_and_get(smmu->dev);
+	if (ret < 0) {
+		dev_err(smmu->dev, "failed to resume device: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+__maybe_unused static bool arm_smmu_rpm_get_if_active(struct arm_smmu_device *smmu)
+{
+	if (!pm_runtime_enabled(smmu->dev))
+		return true;
+
+	return pm_runtime_get_if_active(smmu->dev) > 0;
+}
+
+__maybe_unused static void arm_smmu_rpm_put(struct arm_smmu_device *smmu)
+{
+	int ret;
+
+	if (!pm_runtime_enabled(smmu->dev))
+		return;
+
+	ret = pm_runtime_put_autosuspend(smmu->dev);
+
+	/* -EAGAIN & -EBUSY aren't failures */
+	if (ret < 0 && ret != -EAGAIN && ret != -EBUSY)
+		dev_err(smmu->dev, "failed to suspend device: %d\n", ret);
+}

+	/* Wait for the last committed owner to reach the hardware */
+	while (atomic_read(&cmdq->owner_prod) != target && timeout) {
+		udelay(1);
+		timeout--;
+	}
+
+	/*
+	 * Entering suspend implies no active clients. A timeout here
+	 * indicates a fatal CMDQ lockup or hardware stall. We proceed
+	 * anyway to prioritize memory safety (avoiding stale TLBs)
+	 */
+	if (!timeout)
+		dev_err(smmu->dev, "cmdq owner wait timeout, (check runtime PM + devlinks)\n");
+
+	/* Wait for cmdq->lock == 0 to ensure last CMDQ_CONS_REG is written */
+	timeout = ARM_SMMU_SUSPEND_TIMEOUT_US;
+	while (atomic_read(&cmdq->lock) != 0 && timeout) {
+		udelay(1);
+		timeout--;
+	}
+
+	/* Timing out here implies misconfigured Runtime PM or broken devlinks */
+	if (!timeout)
+		dev_err(smmu->dev, "cmdq lock != 0, forcing suspend. Polling CPUs may fault.\n");