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Subject[PATCH v2 2/2] dmaengine: Add basic debugfs support
Date
Via the /sys/kernel/debug/dmaengine 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 6 channels:

# cat /sys/kernel/debug/dmaengine
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
dma1chan6: in-use
dma1chan7: 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_show callback to provide
controller specific information instead of the generic one.

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

I have taken the idea from gpiolib.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
---
drivers/dma/dmaengine.c | 66 +++++++++++++++++++++++++++++++++++++++
include/linux/dmaengine.h | 12 ++++++-
2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 342d23132fca..121231300d35 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -32,6 +32,7 @@
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/platform_device.h>
+#include <linux/debugfs.h>
#include <linux/dma-mapping.h>
#include <linux/init.h>
#include <linux/module.h>
@@ -760,6 +761,11 @@ 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 +843,11 @@ 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);
@@ -1559,3 +1570,58 @@ static int __init dma_bus_init(void)
return class_register(&dma_devclass);
}
arch_initcall(dma_bus_init);
+
+#ifdef CONFIG_DEBUG_FS
+static void dmaengine_dbg_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, " dma%dchan%-4d| %s",
+ dma_dev->dev_id, chan->chan_id,
+ 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_debugfs_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_show)
+ dma_dev->dbg_show(s, dma_dev);
+ else
+ dmaengine_dbg_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_debugfs);
+
+static int __init dmaengine_debugfs_init(void)
+{
+ /* /sys/kernel/debug/dmaengine */
+ debugfs_create_file("dmaengine", 0444, NULL, NULL,
+ &dmaengine_debugfs_fops);
+ return 0;
+}
+late_initcall(dmaengine_debugfs_init);
+
+#endif /* DEBUG_FS */
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 64461fc64e1b..9f232b7618f1 100644
--- a/include/linux/dmaengine.h
+++ b/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;
@@ -805,7 +810,9 @@ 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_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;
@@ -891,6 +898,9 @@ struct dma_device {
struct dma_tx_state *txstate);
void (*device_issue_pending)(struct dma_chan *chan);
void (*device_release)(struct dma_device *dev);
+#ifdef CONFIG_DEBUG_FS
+ void (*dbg_show)(struct seq_file *s, struct dma_device *dev);
+#endif
};

static inline int dmaengine_slave_config(struct dma_chan *chan,
--
Peter
Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

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