dmaengine: Create debug directories for DMA devices

Create a placeholder directory for each registered DMA device.

DMA drivers can use the dmaengine_get_debugfs_root() call to get their
debugfs root and can populate with custom files to aim debugging.

Signed-off-by: Peter Ujfalusi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Vinod Koul <[e-mail]>

drivers/dma/dmaengine.c

···
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
 
+static struct dentry *rootdir;
+
+static void dmaengine_debug_register(struct dma_device *dma_dev)
+{
+	dma_dev->dbg_dev_root = debugfs_create_dir(dev_name(dma_dev->dev),
+						   rootdir);
+	if (IS_ERR(dma_dev->dbg_dev_root))
+		dma_dev->dbg_dev_root = NULL;
+}
+
+static void dmaengine_debug_unregister(struct dma_device *dma_dev)
+{
+	debugfs_remove_recursive(dma_dev->dbg_dev_root);
+	dma_dev->dbg_dev_root = NULL;
+}
+
 static void dmaengine_dbg_summary_show(struct seq_file *s,
 				       struct dma_device *dma_dev)
 {
···
 
 static void __init dmaengine_debugfs_init(void)
 {
-	struct dentry *rootdir = debugfs_create_dir("dmaengine", NULL);
+	rootdir = debugfs_create_dir("dmaengine", NULL);
 
 	/* /sys/kernel/debug/dmaengine/summary */
 	debugfs_create_file("summary", 0444, rootdir, NULL,
···
 }
 #else
 static inline void dmaengine_debugfs_init(void) { }
+static inline int dmaengine_debug_register(struct dma_device *dma_dev)
+{
+	return 0;
+}
+
+static inline void dmaengine_debug_unregister(struct dma_device *dma_dev) { }
 #endif	/* DEBUG_FS */
 
 /* --- sysfs implementation --- */
···
 	dma_channel_rebalance();
 	mutex_unlock(&dma_list_mutex);
 
+	dmaengine_debug_register(device);
+
 	return 0;
 
 err_out:
···
 void dma_async_device_unregister(struct dma_device *device)
 {
 	struct dma_chan *chan, *n;
+
+	dmaengine_debug_unregister(device);
 
 	list_for_each_entry_safe(chan, n, &device->channels, device_node)
 		__dma_async_device_channel_unregister(device, chan);

drivers/dma/dmaengine.h

···
 struct dma_chan *dma_get_slave_channel(struct dma_chan *chan);
 struct dma_chan *dma_get_any_slave_channel(struct dma_device *device);
 
+#ifdef CONFIG_DEBUG_FS
+#include <linux/debugfs.h>
+
+static inline struct dentry *
+dmaengine_get_debugfs_root(struct dma_device *dma_dev) {
+	return dma_dev->dbg_dev_root;
+}
+#else
+struct dentry;
+static inline struct dentry *
+dmaengine_get_debugfs_root(struct dma_device *dma_dev)
+{
+	return NULL;
+}
+#endif /* CONFIG_DEBUG_FS */
+
 #endif

include/linux/dmaengine.h

···
 	/* debugfs support */
 #ifdef CONFIG_DEBUG_FS
 	void (*dbg_summary_show)(struct seq_file *s, struct dma_device *dev);
+	struct dentry *dbg_dev_root;
 #endif
 };