[PATCH v2 2/4] iommu/arm-smmu-v3: Enable an optional clock

[Arun Iyengar via B4 Relay <devnull+aiyengar1990.gmail.com@kernel.org>]

From: Arun Iyengar <aiyengar1990@gmail.com>

On some platforms the SMMU's clock is controlled by the OS, and without a
consumer the clock framework gates it as unused late in boot. Any later
register access, for example the CR0 write in the shutdown path, then
hangs. This happens on the RK3588 when no PCIe controller keeps the PCIe
MMU-600 clock running.

Get and enable the clock described in the firmware node, if there is
one, and keep it enabled while the driver is bound. Do it first in
probe: the firmware probe may take a reference on the Tegra CMDQV device
that only arm_smmu_impl_probe() releases, so a failure (or deferral)
between the two would leak it. Nodes without a clock and ACPI systems
are not affected.

Signed-off-by: Arun Iyengar <aiyengar1990@gmail.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

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 6d4520c47308..d3f42316b0d6 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -12,6 +12,7 @@
 #include <linux/acpi.h>
 #include <linux/acpi_iort.h>
 #include <linux/bitops.h>
+#include <linux/clk.h>
 #include <linux/crash_dump.h>
 #include <linux/delay.h>
 #include <linux/err.h>
@@ -5786,12 +5787,22 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
 	resource_size_t ioaddr;
 	struct arm_smmu_device *smmu;
 	struct device *dev = &pdev->dev;
+	struct clk *clk;
 
 	smmu = devm_kzalloc(dev, sizeof(*smmu), GFP_KERNEL);
 	if (!smmu)
 		return -ENOMEM;
 	smmu->dev = dev;
 
+	/*
+	 * Before the firmware probe: it may take a reference on the Tegra
+	 * CMDQV device that only arm_smmu_impl_probe() releases.
+	 */
+	clk = devm_clk_get_optional_enabled(dev, NULL);
+	if (IS_ERR(clk))
+		return dev_err_probe(dev, PTR_ERR(clk),
+				     "failed to enable clock\n");
+
 	if (dev->of_node) {
 		ret = arm_smmu_device_dt_probe(pdev, smmu);
 	} else {

-- 
2.55.0