[RFC PATCH 1/5] iommu/arm-smmu-v3: Add basic debugfs framework
Qinxin Xia
xiaqinxin at huawei.com
Fri Mar 13 03:43:47 PDT 2026
Add basic debugfs framework for ARM SMMUv3 driver.This creates the
root directory structure and provides capability display functionality.
The debugfs hierarchy is organized as:
/sys/kernel/debug/iommu/arm_smmu_v3/
└── smmu0/
└── capabilities
Signed-off-by: Qinxin Xia <xiaqinxin at huawei.com>
---
drivers/iommu/Kconfig | 11 ++
drivers/iommu/arm/arm-smmu-v3/Makefile | 1 +
.../arm/arm-smmu-v3/arm-smmu-v3-debugfs.c | 132 ++++++++++++++++++
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 10 ++
drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h | 14 ++
5 files changed, 168 insertions(+)
create mode 100644 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-debugfs.c
diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index f86262b11416..dfde3779764a 100644
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -93,6 +93,17 @@ config IOMMU_DEBUGFS
debug/iommu directory, and then populate a subdirectory with
entries as required.
+config ARM_SMMU_V3_DEBUGFS
+ bool "ARM SMMUv3 DebugFS support"
+ depends on ARM_SMMU_V3 && IOMMU_DEBUGFS
+ help
+ Expose ARM SMMUv3 internal state via debugfs for debugging and
+ diagnostics. This creates /sys/kernel/debug/arm_smmu_v3/ with
+ detailed information about SMMU configuration, stream tables,
+ and context descriptors.
+
+ Say N unless you are debugging IOMMU issues.
+
choice
prompt "IOMMU default domain type"
depends on IOMMU_API
diff --git a/drivers/iommu/arm/arm-smmu-v3/Makefile b/drivers/iommu/arm/arm-smmu-v3/Makefile
index 493a659cc66b..81fd2808f12f 100644
--- a/drivers/iommu/arm/arm-smmu-v3/Makefile
+++ b/drivers/iommu/arm/arm-smmu-v3/Makefile
@@ -6,3 +6,4 @@ arm_smmu_v3-$(CONFIG_ARM_SMMU_V3_SVA) += arm-smmu-v3-sva.o
arm_smmu_v3-$(CONFIG_TEGRA241_CMDQV) += tegra241-cmdqv.o
obj-$(CONFIG_ARM_SMMU_V3_KUNIT_TEST) += arm-smmu-v3-test.o
+obj-$(CONFIG_ARM_SMMU_V3_DEBUGFS) += arm-smmu-v3-debugfs.o
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-debugfs.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-debugfs.c
new file mode 100644
index 000000000000..542bd6047f26
--- /dev/null
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-debugfs.c
@@ -0,0 +1,132 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ARM SMMUv3 DebugFS Support
+ *
+ * This file implements the basic debugfs infrastructure for ARM SMMUv3 driver.
+ * It provides the foundation for exposing SMMU internal state through debugfs
+ * for debugging and diagnostic purposes.
+ *
+ * Key Features:
+ * - Global root directory management with proper mutex synchronization
+ * - Per-SMMU instance directory creation with unique naming
+ * - Capability reporting covering all major SMMU features and configuration
+ * - Extensible architecture designed for adding future debug functionality
+ * - Comprehensive error handling and resource cleanup
+ *
+ * Directory Structure:
+ * /sys/kernel/debug/iommu/arm_smmu_v3/
+ * └── smmu0/
+ * └── capabilities # SMMU feature capabilities and configuration
+ *
+ * The capabilities file provides detailed information about:
+ * - Architecture version and translation stage support (Stage1/Stage2)
+ * - System coherency, ATS, and PRI feature availability
+ * - Stream table size and command/event queue depths
+ * - All feature bits from the SMMU device structure
+ *
+ * Copyright (C) 2025 HiSilicon Limited.
+ * Author: Qinxin Xia <xiaqinxin at huawei.com>
+ */
+
+#include <linux/debugfs.h>
+#include "arm-smmu-v3.h"
+
+static struct dentry *smmuv3_root_dir;
+static DEFINE_MUTEX(arm_smmu_debugfs_lock);
+
+/**
+ * smmu_debugfs_capabilities_show() - Display SMMU capabilities
+ * @seq: seq_file to write to
+ * @v: private data (SMMU device)
+ *
+ * Return: 0 on success, negative error code on failure
+ */
+static int smmu_debugfs_capabilities_show(struct seq_file *seq, void *v)
+{
+ struct arm_smmu_device *smmu = seq->private;
+
+ if (!smmu)
+ return -ENODEV;
+
+ seq_puts(seq, "SMMUv3 Capabilities:\n");
+ seq_printf(seq, " Stage1 Translation: %s\n",
+ smmu->features & ARM_SMMU_FEAT_TRANS_S1 ? "Yes" : "No");
+ seq_printf(seq, " Stage2 Translation: %s\n",
+ smmu->features & ARM_SMMU_FEAT_TRANS_S2 ? "Yes" : "No");
+ seq_printf(seq, " Coherent Walk: %s\n",
+ smmu->features & ARM_SMMU_FEAT_COHERENCY ? "Yes" : "No");
+ seq_printf(seq, " ATS Support: %s\n",
+ smmu->features & ARM_SMMU_FEAT_ATS ? "Yes" : "No");
+ seq_printf(seq, " PRI Support: %s\n",
+ smmu->features & ARM_SMMU_FEAT_PRI ? "Yes" : "No");
+ seq_printf(seq, " Stream Table Size: %d\n", 1 << smmu->sid_bits);
+ seq_printf(seq, " Command Queue Depth: %d\n",
+ 1 << smmu->cmdq.q.llq.max_n_shift);
+ seq_printf(seq, " Event Queue Depth: %d\n",
+ 1 << smmu->evtq.q.llq.max_n_shift);
+
+ return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(smmu_debugfs_capabilities);
+
+/**
+ * arm_smmu_debugfs_setup() - Initialize debugfs for SMMU device
+ * @smmu: SMMU device to setup debugfs for
+ * @ioaddr: Physical base address of the SMMU device registers
+ *
+ * This function creates the basic debugfs directory structure for a SMMU device.
+ *
+ * Return: 0 on success, negative error code on failure
+ */
+int arm_smmu_debugfs_setup(struct arm_smmu_device *smmu, phys_addr_t ioaddr)
+{
+ struct arm_smmu_debugfs *debugfs;
+ struct dentry *smmu_dir;
+ char name[32];
+ int ret;
+
+ /* Create root directory if it doesn't exist */
+ mutex_lock(&arm_smmu_debugfs_lock);
+ if (!smmuv3_root_dir) {
+ smmuv3_root_dir = debugfs_create_dir("arm_smmu_v3",
+ iommu_debugfs_dir);
+ if (!smmuv3_root_dir) {
+ mutex_unlock(&arm_smmu_debugfs_lock);
+ return -ENOMEM;
+ }
+ }
+ mutex_unlock(&arm_smmu_debugfs_lock);
+
+ /* Allocate debugfs structure */
+ debugfs = kzalloc(sizeof(*debugfs), GFP_KERNEL);
+ if (!debugfs)
+ return -ENOMEM;
+
+ smmu->debugfs = debugfs;
+ debugfs->smmu = smmu;
+
+ /* Create SMMU instance directory */
+ snprintf(name, sizeof(name), "smmu3.%pa", &ioaddr);
+ smmu_dir = debugfs_create_dir(name, smmuv3_root_dir);
+ if (!smmu_dir) {
+ ret = -ENOMEM;
+ goto err_free;
+ }
+
+ debugfs->smmu_dir = smmu_dir;
+
+ /* Create capabilities file */
+ if (!debugfs_create_file("capabilities", 0444, smmu_dir, smmu,
+ &smmu_debugfs_capabilities_fops))
+ goto err_cleanup;
+
+ pr_info("SMMUv3 debugfs initialized for smmu%pa\n", &ioaddr);
+ return 0;
+
+err_cleanup:
+ debugfs_remove_recursive(smmu_dir);
+err_free:
+ kfree(debugfs);
+ smmu->debugfs = NULL;
+ return ret;
+}
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 4d00d796f078..211a0c87507a 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -33,6 +33,10 @@
#include "arm-smmu-v3.h"
#include "../../dma-iommu.h"
+#ifdef CONFIG_ARM_SMMU_V3_DEBUGFS
+static unsigned int arm_smmu_present;
+#endif
+
static bool disable_msipolling;
module_param(disable_msipolling, bool, 0444);
MODULE_PARM_DESC(disable_msipolling,
@@ -4909,6 +4913,12 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
if (ret)
goto err_disable;
+#ifdef CONFIG_ARM_SMMU_V3_DEBUGFS
+ ret = arm_smmu_debugfs_setup(smmu, ioaddr);
+ if (ret)
+ dev_warn(dev, "Failed to create debugfs!\n");
+#endif
+
/* And we're up. Go go go! */
ret = iommu_device_sysfs_add(&smmu->iommu, dev, NULL,
"smmu3.%pa", &ioaddr);
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 3c6d65d36164..247f27426f6b 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -733,6 +733,15 @@ struct arm_smmu_impl_ops {
const struct iommu_user_data *user_data);
};
+#ifdef CONFIG_ARM_SMMU_V3_DEBUGFS
+struct arm_smmu_debugfs {
+ struct dentry *root_dir;
+ struct dentry *smmu_dir;
+ struct arm_smmu_device *smmu;
+};
+int arm_smmu_debugfs_setup(struct arm_smmu_device *smmu, phys_addr_t ioaddr);
+#endif
+
/* An SMMUv3 instance */
struct arm_smmu_device {
struct device *dev;
@@ -803,6 +812,11 @@ struct arm_smmu_device {
struct rb_root streams;
struct mutex streams_mutex;
+
+#ifdef CONFIG_ARM_SMMU_V3_DEBUGFS
+ /* DebugFS Info */
+ struct arm_smmu_debugfs *debugfs;
+#endif
};
struct arm_smmu_stream {
--
2.33.0
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