[PATCH 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>
---
 .../iommu/arm/arm-smmu-v3/arm-smmu-v3-debugfs.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

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 a5866f34264f..9babc7d640fd 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
@@ -10,6 +10,7 @@
  *     ├── stream_table
  *         ├── <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"
 
@@ -314,6 +316,7 @@ int arm_smmu_debugfs_create_stream_table(struct arm_smmu_device *smmu,
 	struct dentry *stream_dir, *dev_dir;
 	struct arm_smmu_master *master;
 	struct ste_context *ctx;
+	char *path = NULL, *full_path;
 	char name[64];
 	u32 sid;
 	int i;
@@ -338,6 +341,9 @@ int arm_smmu_debugfs_create_stream_table(struct arm_smmu_device *smmu,
 	if (!master || !master->num_streams)
 		return -ENODEV;
 
+	/* Get device sysfs path once, reuse for all streams */
+	path = kobject_get_path(&dev->kobj, GFP_KERNEL);
+
 	for (i = 0; i < master->num_streams; i++) {
 		sid = master->streams[i].id;
 		snprintf(name, sizeof(name), "%u", sid);
@@ -357,8 +363,19 @@ int arm_smmu_debugfs_create_stream_table(struct arm_smmu_device *smmu,
 		spin_unlock(&smmu->debugfs->stream_lock);
 		debugfs_create_file("ste", 0444, dev_dir, ctx,
 				    &smmu_debugfs_ste_fops);
+
+		/* Create a symlink to the device's sysfs directory */
+		if (path) {
+			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