Re: [PATCH v6 08/12] dma-buf: heaps: Add debugfs support

Since AMDs mail servers blocked me from sending this out, here once more from my gmail account.

Regards,
Christian.

On 9/4/26 15:00, Christian König wrote:

On 9/4/26 12:44, Thierry Reding wrote:

quoted

From: Thierry Reding <redacted>

Add a callback to struct dma_heap_ops that heap providers can implement
to show information about the state of the heap in debugfs. A top-level
directory named "dma_heap" is created in debugfs and individual files
will be named after the heaps.

Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Thierry Reding <redacted>

One minimal nit pick below, with that taken care of Reviewed-by: Christian König [off-list ref].

quoted

---
Changes in v5:
- fix failure handling during debugfs root directory creation
- add more cleanup to the newly introduced dma_heap_exit()
---
 drivers/dma-buf/dma-heap.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/dma-heap.h   |  2 ++
 2 files changed, 54 insertions(+)

diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
index 8a6c2b6e0cc6..65c80dac6500 100644
--- a/drivers/dma-buf/dma-heap.c
+++ b/drivers/dma-buf/dma-heap.c

@@ -7,6 +7,7 @@
  */
 
 #include <linux/cdev.h>
+#include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/dma-buf.h>
 #include <linux/dma-heap.h>

@@ -225,6 +226,40 @@ const char *dma_heap_get_name(struct dma_heap *heap)
 }
 EXPORT_SYMBOL_NS_GPL(dma_heap_get_name, "DMA_BUF_HEAP");
 
+#ifdef CONFIG_DEBUG_FS
+static int dma_heap_debug_show(struct seq_file *s, void *unused)
+{
+	struct dma_heap *heap = s->private;
+	int err = 0;
+
+	if (heap->ops && heap->ops->show)
+		err = heap->ops->show(s, heap);
+
+	return err;
+}
+DEFINE_SHOW_ATTRIBUTE(dma_heap_debug);
+
+static struct dentry *dma_heap_debugfs_dir;
+
+static void dma_heap_init_debugfs(void)
+{
+	dma_heap_debugfs_dir = debugfs_create_dir("dma_heap", NULL);
+}
+
+static void dma_heap_exit_debugfs(void)
+{
+	debugfs_remove_recursive(dma_heap_debugfs_dir);
+}
+#else
+static void dma_heap_init_debugfs(void)
+{
+}
+
+static void dma_heap_exit_debugfs(void)
+{
+}
+#endif
+
 /**
  * dma_heap_add - adds a heap to dmabuf heaps
  * @exp_info: information needed to register this heap

@@ -299,6 +334,13 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
 
 	/* Add heap to the list */
 	list_add(&heap->list, &heap_list);
+
+#ifdef CONFIG_DEBUG_FS
+	if (heap->ops && heap->ops->show)
+		debugfs_create_file(heap->name, 0444, dma_heap_debugfs_dir,
+				    heap, &dma_heap_debug_fops);
+#endif
+
 	mutex_unlock(&heap_list_lock);
 
 	return heap;

@@ -335,6 +377,16 @@ static int dma_heap_init(void)
 	}
 	dma_heap_class->devnode = dma_heap_devnode;
 
+	dma_heap_init_debugfs();
+
 	return 0;
 }
 subsys_initcall(dma_heap_init);
+
+static void __exit dma_heap_exit(void)
+{
+	dma_heap_exit_debugfs();
+	class_destroy(dma_heap_class);
+	unregister_chrdev_region(dma_heap_devt, NUM_HEAP_MINORS);
+}
+__exitcall(dma_heap_exit);

diff --git a/include/linux/dma-heap.h b/include/linux/dma-heap.h
index 648328a64b27..1c9bed1f4dde 100644
--- a/include/linux/dma-heap.h
+++ b/include/linux/dma-heap.h

@@ -12,6 +12,7 @@
 #include <linux/types.h>
 
 struct dma_heap;
+struct seq_file;
 
 /**
  * struct dma_heap_ops - ops to operate on a given heap

@@ -24,6 +25,7 @@ struct dma_heap_ops {
 				    unsigned long len,
 				    u32 fd_flags,
 				    u64 heap_flags);
+	int (*show)(struct seq_file *s, struct dma_heap *heap);

I found it good coding practice for objects ops pointer tables to have the object the function works with as first parameter.

Absolutely not a must have, but just looks a little bit more consistent.

Regards,
Christian.

quoted

 };
 
 /**

On Wed, Sep 09, 2026 at 01:04:03PM +0200, Christian König wrote:

Since AMDs mail servers blocked me from sending this out, here once more from my gmail account.

Regards,
Christian.

On 9/4/26 15:00, Christian König wrote:

quoted

On 9/4/26 12:44, Thierry Reding wrote:

quoted

From: Thierry Reding <redacted>

Add a callback to struct dma_heap_ops that heap providers can implement
to show information about the state of the heap in debugfs. A top-level
directory named "dma_heap" is created in debugfs and individual files
will be named after the heaps.

Reviewed-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Thierry Reding <redacted>

One minimal nit pick below, with that taken care of Reviewed-by: Christian König [off-list ref].

quoted

---
Changes in v5:
- fix failure handling during debugfs root directory creation
- add more cleanup to the newly introduced dma_heap_exit()
---
 drivers/dma-buf/dma-heap.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/dma-heap.h   |  2 ++
 2 files changed, 54 insertions(+)

diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
index 8a6c2b6e0cc6..65c80dac6500 100644
--- a/drivers/dma-buf/dma-heap.c
+++ b/drivers/dma-buf/dma-heap.c

@@ -7,6 +7,7 @@
  */
 
 #include <linux/cdev.h>
+#include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/dma-buf.h>
 #include <linux/dma-heap.h>

@@ -225,6 +226,40 @@ const char *dma_heap_get_name(struct dma_heap *heap)
 }
 EXPORT_SYMBOL_NS_GPL(dma_heap_get_name, "DMA_BUF_HEAP");
 
+#ifdef CONFIG_DEBUG_FS
+static int dma_heap_debug_show(struct seq_file *s, void *unused)
+{
+	struct dma_heap *heap = s->private;
+	int err = 0;
+
+	if (heap->ops && heap->ops->show)
+		err = heap->ops->show(s, heap);
+
+	return err;
+}
+DEFINE_SHOW_ATTRIBUTE(dma_heap_debug);
+
+static struct dentry *dma_heap_debugfs_dir;
+
+static void dma_heap_init_debugfs(void)
+{
+	dma_heap_debugfs_dir = debugfs_create_dir("dma_heap", NULL);
+}
+
+static void dma_heap_exit_debugfs(void)
+{
+	debugfs_remove_recursive(dma_heap_debugfs_dir);
+}
+#else
+static void dma_heap_init_debugfs(void)
+{
+}
+
+static void dma_heap_exit_debugfs(void)
+{
+}
+#endif
+
 /**
  * dma_heap_add - adds a heap to dmabuf heaps
  * @exp_info: information needed to register this heap

@@ -299,6 +334,13 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
 
 	/* Add heap to the list */
 	list_add(&heap->list, &heap_list);
+
+#ifdef CONFIG_DEBUG_FS
+	if (heap->ops && heap->ops->show)
+		debugfs_create_file(heap->name, 0444, dma_heap_debugfs_dir,
+				    heap, &dma_heap_debug_fops);
+#endif
+
 	mutex_unlock(&heap_list_lock);
 
 	return heap;

@@ -335,6 +377,16 @@ static int dma_heap_init(void)
 	}
 	dma_heap_class->devnode = dma_heap_devnode;
 
+	dma_heap_init_debugfs();
+
 	return 0;
 }
 subsys_initcall(dma_heap_init);
+
+static void __exit dma_heap_exit(void)
+{
+	dma_heap_exit_debugfs();
+	class_destroy(dma_heap_class);
+	unregister_chrdev_region(dma_heap_devt, NUM_HEAP_MINORS);
+}
+__exitcall(dma_heap_exit);

diff --git a/include/linux/dma-heap.h b/include/linux/dma-heap.h
index 648328a64b27..1c9bed1f4dde 100644
--- a/include/linux/dma-heap.h
+++ b/include/linux/dma-heap.h

@@ -12,6 +12,7 @@
 #include <linux/types.h>
 
 struct dma_heap;
+struct seq_file;
 
 /**
  * struct dma_heap_ops - ops to operate on a given heap

@@ -24,6 +25,7 @@ struct dma_heap_ops {
 				    unsigned long len,
 				    u32 fd_flags,
 				    u64 heap_flags);
+	int (*show)(struct seq_file *s, struct dma_heap *heap);

I found it good coding practice for objects ops pointer tables to have the object the function works with as first parameter.

Absolutely not a must have, but just looks a little bit more consistent.

Agreed, I generally prefer that too. However, in this case I thought it
more important to model this after how pretty much every debugfs file
operation works, which is to take the seq_file as first parameter. It's
the same order as for the main dma_heap_debug_show() entry point that
this is called from, so it's consistent that way.

I guess an alternative way to think about it is that in this case the
object that we're really working with is the seq_file and the dma_heap
is what gets written to that seq_file.

Thierry