[RFC PATCH v2 4/5] iommu/arm-smmu-v3: Add device symlink in stream table debugfs

[Qinxin Xia <xiaqinxin@huawei.com>]

Add a symlink named  under each stream table entry directory pointing to
the sysfs directory of the actual device. This aids debugging
by providing direct access to device attributes.

/sys/kernel/debug/iommu/arm_smmu_v3/smmu0/stream_table/
└── <sid>/
    ├─── ste
    └─── <dev_name>

Signed-off-by: Qinxin Xia <xiaqinxin@huawei.com>
---
 .../arm/arm-smmu-v3/arm-smmu-v3-debugfs.c     | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

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
index 70623b480d64..dbcc8fce6d8e 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-debugfs.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-debugfs.c
@@ -8,8 +8,9 @@
  *     ├── capabilities    # SMMU feature capabilities and configuration
  *     ├── registers	   # SMMU Key registers
  *     └── stream_table
- *	   └─── <sid>/                                # Stream ID 0
- *	       └── ste                                # Stream Table Entry
+ *	   └─── <sid>/                                # Stream ID
+ *	       ├─── ste                               # Stream Table Entry
+ *	       └── <dev_name>                         # Symlink to device sysfs directory
  *
  * The capabilities file provides detailed information about:
  * - translation stage support (Stage1/Stage2)
@@ -31,6 +32,7 @@
 
 #include <linux/cleanup.h>
 #include <linux/debugfs.h>
+#include <linux/kobject.h>
 #include <linux/slab.h>
 #include "arm-smmu-v3.h"
 
@@ -295,6 +297,7 @@ int arm_smmu_debugfs_create_stream_table(struct device *dev,
 	struct dentry *stream_dir, *dev_dir;
 	struct arm_smmu_master *master;
 	struct ste_context *ctx;
+	char *path, *full_path;
 	char name[64];
 	u32 sid;
 	int i;
@@ -333,6 +336,18 @@ int arm_smmu_debugfs_create_stream_table(struct device *dev,
 		debugfs_create_file("ste", 0444, dev_dir, ctx,
 				    &smmu_debugfs_ste_fops);
 
+		/* Create a symlink to the device's sysfs directory */
+		path = kobject_get_path(&dev->kobj, GFP_KERNEL);
+		if (!path)
+			continue;
+
+		full_path = kasprintf(GFP_KERNEL, "/sys%s", path);
+		if (full_path) {
+			debugfs_create_symlink(dev_name(dev), dev_dir, full_path);
+			kfree(full_path);
+		}
+
+		kfree(path);
 	}
 
 	return 0;
-- 
2.33.0