[PATCH 7/8] iommu/qcom: Enable clocks before hardware access in qcom_iommu_ctx_probe()

[Mukesh Ojha]

qcom_iommu_ctx_probe() reads and writes the CB_FSR register to clear any
stale IRQ left by the bootloader. This happens during
devm_of_platform_populate() which is called from the parent device's
probe before any pm_runtime_get(). The parent's clocks (iface, bus, tbu)
are therefore not guaranteed to be on, making the register access
unreliable on rebind or after a suspend cycle.

Use pm_runtime_resume_and_get() on the parent device to ensure clocks
are enabled before the register access, and release the reference
immediately after.

Signed-off-by: Mukesh Ojha <mukesh.ojha@xxxxxxxxxxxxxxxx>
---
 drivers/iommu/arm/arm-smmu/qcom_iommu.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/arm/arm-smmu/qcom_iommu.c b/drivers/iommu/arm/arm-smmu/qcom_iommu.c
index 51b60b296bb8..0df8c2af8eed 100644
--- a/drivers/iommu/arm/arm-smmu/qcom_iommu.c
+++ b/drivers/iommu/arm/arm-smmu/qcom_iommu.c
@@ -714,8 +714,13 @@ static int qcom_iommu_ctx_probe(struct platform_device *pdev)
 	/* clear IRQs before registering fault handler, just in case the
 	 * boot-loader left us a surprise:
 	 */
-	if (!ctx->secured_ctx)
+	if (!ctx->secured_ctx) {
+		ret = pm_runtime_resume_and_get(dev->parent);
+		if (ret)
+			return ret;
 		iommu_writel(ctx, ARM_SMMU_CB_FSR, iommu_readl(ctx, ARM_SMMU_CB_FSR));
+		pm_runtime_put_sync(dev->parent);
+	}
 
 	ret = devm_request_irq(dev, irq,
 			       qcom_iommu_fault,
-- 
2.53.0