dmaengine: Add basic debugfs support

Via the /sys/kernel/debug/dmaengine/summary users can get information
about the DMA devices and the used channels.

Example output on am654-evm with audio using two channels and after running
dmatest on 4 channels:

dma0 (285c0000.dma-controller): number of channels: 96

dma1 (31150000.dma-controller): number of channels: 267
 dma1chan0    | 2b00000.mcasp:tx
 dma1chan1    | 2b00000.mcasp:rx
 dma1chan2    | in-use
 dma1chan3    | in-use
 dma1chan4    | in-use
 dma1chan5    | in-use

For slave channels we can show the device and the channel name a given
channel is requested.
For non slave devices the only information we know is that the channel is
in use.

DMA drivers can implement the optional dbg_summary_show callback to
provide controller specific information instead of the generic one.

It is easy to extend the generic dmaengine_summary_show() to print
additional information about the used channels.

I have taken the idea from gpiolib and clk subsystems.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20200306142839.17910-2-peter.ujfalusi@ti.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/dmaengine.c

@@ -58,6 +58,65 @@ static DEFINE_IDA(dma_ida);
 static LIST_HEAD(dma_device_list);
 static long dmaengine_ref_count;
 
+/* --- debugfs implementation --- */
+#ifdef CONFIG_DEBUG_FS
+#include <linux/debugfs.h>
+
+static void dmaengine_dbg_summary_show(struct seq_file *s,
+				       struct dma_device *dma_dev)
+{
+	struct dma_chan *chan;
+
+	list_for_each_entry(chan, &dma_dev->channels, device_node) {
+		if (chan->client_count) {
+			seq_printf(s, " %-13s| %s", dma_chan_name(chan),
+				   chan->dbg_client_name ?: "in-use");
+
+			if (chan->router)
+				seq_printf(s, " (via router: %s)\n",
+					dev_name(chan->router->dev));
+			else
+				seq_puts(s, "\n");
+		}
+	}
+}
+
+static int dmaengine_summary_show(struct seq_file *s, void *data)
+{
+	struct dma_device *dma_dev = NULL;
+
+	mutex_lock(&dma_list_mutex);
+	list_for_each_entry(dma_dev, &dma_device_list, global_node) {
+		seq_printf(s, "dma%d (%s): number of channels: %u\n",
+			   dma_dev->dev_id, dev_name(dma_dev->dev),
+			   dma_dev->chancnt);
+
+		if (dma_dev->dbg_summary_show)
+			dma_dev->dbg_summary_show(s, dma_dev);
+		else
+			dmaengine_dbg_summary_show(s, dma_dev);
+
+		if (!list_is_last(&dma_dev->global_node, &dma_device_list))
+			seq_puts(s, "\n");
+	}
+	mutex_unlock(&dma_list_mutex);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(dmaengine_summary);
+
+static void __init dmaengine_debugfs_init(void)
+{
+	struct dentry *rootdir = debugfs_create_dir("dmaengine", NULL);
+
+	/* /sys/kernel/debug/dmaengine/summary */
+	debugfs_create_file("summary", 0444, rootdir, NULL,
+			    &dmaengine_summary_fops);
+}
+#else
+static inline void dmaengine_debugfs_init(void) { }
+#endif	/* DEBUG_FS */
+
 /* --- sysfs implementation --- */
 
 #define DMA_SLAVE_NAME	"slave"
@@ -760,6 +819,11 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
 		return chan ? chan : ERR_PTR(-EPROBE_DEFER);
 
 found:
+#ifdef CONFIG_DEBUG_FS
+	chan->dbg_client_name = kasprintf(GFP_KERNEL, "%s:%s", dev_name(dev),
+					  name);
+#endif
+
 	chan->name = kasprintf(GFP_KERNEL, "dma:%s", name);
 	if (!chan->name)
 		return chan;
@@ -837,6 +901,11 @@ void dma_release_channel(struct dma_chan *chan)
 		chan->name = NULL;
 		chan->slave = NULL;
 	}
+
+#ifdef CONFIG_DEBUG_FS
+	kfree(chan->dbg_client_name);
+	chan->dbg_client_name = NULL;
+#endif
 	mutex_unlock(&dma_list_mutex);
 }
 EXPORT_SYMBOL_GPL(dma_release_channel);
@@ -1559,6 +1628,11 @@ static int __init dma_bus_init(void)
 
 	if (err)
 		return err;
-	return class_register(&dma_devclass);
+
+	err = class_register(&dma_devclass);
+	if (!err)
+		dmaengine_debugfs_init();
+
+	return err;
 }
 arch_initcall(dma_bus_init);

include/linux/dmaengine.h

@@ -300,6 +300,8 @@ struct dma_router {
  * @chan_id: channel ID for sysfs
  * @dev: class device for sysfs
  * @name: backlink name for sysfs
+ * @dbg_client_name: slave name for debugfs in format:
+ *	dev_name(requester's dev):channel name, for example: "2b00000.mcasp:tx"
  * @device_node: used to add this to the device chan list
  * @local: per-cpu pointer to a struct dma_chan_percpu
  * @client_count: how many clients are using this channel
@@ -318,6 +320,9 @@ struct dma_chan {
 	int chan_id;
 	struct dma_chan_dev *dev;
 	const char *name;
+#ifdef CONFIG_DEBUG_FS
+	char *dbg_client_name;
+#endif
 
 	struct list_head device_node;
 	struct dma_chan_percpu __percpu *local;
@@ -806,7 +811,9 @@ struct dma_filter {
  *     called and there are no further references to this structure. This
  *     must be implemented to free resources however many existing drivers
  *     do not and are therefore not safe to unbind while in use.
- *
+ * @dbg_summary_show: optional routine to show contents in debugfs; default code
+ *     will be used when this is omitted, but custom code can show extra,
+ *     controller specific information.
  */
 struct dma_device {
 	struct kref ref;
@@ -892,6 +899,10 @@ struct dma_device {
 					    struct dma_tx_state *txstate);
 	void (*device_issue_pending)(struct dma_chan *chan);
 	void (*device_release)(struct dma_device *dev);
+	/* debugfs support */
+#ifdef CONFIG_DEBUG_FS
+	void (*dbg_summary_show)(struct seq_file *s, struct dma_device *dev);
+#endif
 };
 
 static inline int dmaengine_slave_config(struct dma_chan *chan,