[PATCH 3/9] iio: backend: add debugFs interface

[Nuno Sa <nuno.sa@analog.com>]

This adds a basic debugfs interface for backends. Two new ops are being
added:

 * debugfs_reg_access: Analogous to the core IIO one but for backend
   devices.
 * debugfs_print_chan_status: One useful usecase for this one is for
   testing test tones in a digital interface and "ask" the backend to
   dump more details on why a test tone might have errors.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 drivers/iio/industrialio-backend.c | 115 +++++++++++++++++++++++++++++++++++++
 include/linux/iio/backend.h        |  16 +++++-
 2 files changed, 130 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
index f9da635cdfea..52cbde0d5885 100644
--- a/drivers/iio/industrialio-backend.c
+++ b/drivers/iio/industrialio-backend.c
@@ -32,6 +32,7 @@
 #define dev_fmt(fmt) "iio-backend: " fmt
 
 #include <linux/cleanup.h>
+#include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/errno.h>
@@ -46,6 +47,8 @@
 #include <linux/iio/backend.h>
 #include <linux/iio/iio.h>
 
+#define IIO_BACKEND_DEFAULT_NAME	"backend"
+
 struct iio_backend {
 	struct list_head entry;
 	const struct iio_backend_ops *ops;
@@ -53,6 +56,8 @@ struct iio_backend {
 	struct device *dev;
 	struct module *owner;
 	void *priv;
+	const char *name;
+	unsigned int cached_reg_addr;
 };
 
 /*
@@ -117,6 +122,111 @@ static DEFINE_MUTEX(iio_back_lock);
 			__stringify(op));			\
 }
 
+static ssize_t iio_backend_debugfs_read_reg(struct file *file,
+					    char __user *userbuf,
+					    size_t count, loff_t *ppos)
+{
+	struct iio_backend *back = file->private_data;
+	char read_buf[20];
+	unsigned int val;
+	int ret, len;
+
+	ret = iio_backend_op_call(back, debugfs_reg_access,
+				  back->cached_reg_addr, 0, &val);
+	if (ret)
+		return ret;
+
+	len = scnprintf(read_buf, sizeof(read_buf), "0x%X\n", val);
+
+	return simple_read_from_buffer(userbuf, count, ppos, read_buf, len);
+}
+
+static ssize_t iio_backend_debugfs_write_reg(struct file *file,
+					     const char __user *userbuf,
+					     size_t count, loff_t *ppos)
+{
+	struct iio_backend *back = file->private_data;
+	unsigned int val;
+	char buf[80];
+	ssize_t rc;
+	int ret;
+
+	rc = simple_write_to_buffer(buf, sizeof(buf), ppos, userbuf, count);
+	if (rc < 0)
+		return rc;
+
+	ret = sscanf(buf, "%i %i", &back->cached_reg_addr, &val);
+
+	switch (ret) {
+	case 1:
+		return count;
+	case 2:
+		ret = iio_backend_op_call(back, debugfs_reg_access,
+					  back->cached_reg_addr, val, NULL);
+		if (ret)
+			return ret;
+		return count;
+	default:
+		return -EINVAL;
+	}
+}
+
+static const struct file_operations iio_backend_debugfs_reg_fops = {
+	.open = simple_open,
+	.read = iio_backend_debugfs_read_reg,
+	.write = iio_backend_debugfs_write_reg,
+};
+
+/**
+ * iio_backend_debugfs_add - Add debugfs interfaces for Backends
+ * @back: Backend device
+ * @indio_dev: IIO device
+ */
+void iio_backend_debugfs_add(struct iio_backend *back,
+			     struct iio_dev *indio_dev)
+{
+	struct dentry *d = iio_get_debugfs_dentry(indio_dev);
+	char attr_name[128];
+
+	if (!IS_ENABLED(CONFIG_DEBUG_FS))
+		return;
+	if (!back->ops->debugfs_reg_access || !d)
+		return;
+
+	snprintf(attr_name, sizeof(attr_name), "%s_direct_reg_access",
+		 back->name);
+
+	debugfs_create_file(attr_name, 0644, d, back,
+			    &iio_backend_debugfs_reg_fops);
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_debugfs_add, IIO_BACKEND);
+
+/**
+ * iio_backend_debugfs_print_chan_status - Print channel status
+ * @back: Backend device
+ * @chan: Channel number
+ * @buf: Buffer where to print the status
+ * @len: Available space
+ *
+ * One usecase where this is useful is for testing test tones in a digital
+ * interface and "ask" the backend to dump more details on why a test tone might
+ * have errors.
+ *
+ * RETURNS:
+ * Number of copied bytes on success, negative error code on failure.
+ */
+ssize_t iio_backend_debugfs_print_chan_status(struct iio_backend *back,
+					      unsigned int chan, char *buf,
+					      size_t len)
+{
+	if (!IS_ENABLED(CONFIG_DEBUG_FS))
+		return -ENODEV;
+
+	return iio_backend_op_call(back, debugfs_print_chan_status, chan, buf,
+				   len);
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_debugfs_print_chan_status, IIO_BACKEND);
+
 /**
  * iio_backend_chan_enable - Enable a backend channel
  * @back: Backend device
@@ -577,6 +687,11 @@ struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
 		if (ret)
 			return ERR_PTR(ret);
 
+		if (name)
+			back->name = name;
+		else
+			back->name = IIO_BACKEND_DEFAULT_NAME;
+
 		return back;
 	}
 
diff --git a/include/linux/iio/backend.h b/include/linux/iio/backend.h
index 4e81931703ab..a643d86c7487 100644
--- a/include/linux/iio/backend.h
+++ b/include/linux/iio/backend.h
@@ -9,6 +9,7 @@ struct fwnode_handle;
 struct iio_backend;
 struct device;
 struct iio_dev;
+struct dentry *d;
 
 enum iio_backend_data_type {
 	IIO_BACKEND_TWOS_COMPLEMENT,
@@ -22,6 +23,8 @@ enum iio_backend_data_source {
 	IIO_BACKEND_DATA_SOURCE_MAX
 };
 
+#define iio_backend_debugfs_ptr(ptr)	PTR_IF(IS_ENABLED(CONFIG_DEBUG_FS), ptr)
+
 /**
  * IIO_BACKEND_EX_INFO - Helper for an IIO extended channel attribute
  * @_name: Attribute name
@@ -81,6 +84,8 @@ enum iio_backend_sample_trigger {
  * @extend_chan_spec: Extend an IIO channel.
  * @ext_info_set: Extended info setter.
  * @ext_info_get: Extended info getter.
+ * @debugfs_print_chan_status: Print channel status into a buffer.
+ * @debugfs_reg_access: Read or write register value of backend.
  **/
 struct iio_backend_ops {
 	int (*enable)(struct iio_backend *back);
@@ -113,6 +118,11 @@ struct iio_backend_ops {
 			    const char *buf, size_t len);
 	int (*ext_info_get)(struct iio_backend *back, uintptr_t private,
 			    const struct iio_chan_spec *chan, char *buf);
+	int (*debugfs_print_chan_status)(struct iio_backend *back,
+					 unsigned int chan, char *buf,
+					 size_t len);
+	int (*debugfs_reg_access)(struct iio_backend *back, unsigned int reg,
+				  unsigned int writeval, unsigned int *readval);
 };
 
 int iio_backend_chan_enable(struct iio_backend *back, unsigned int chan);
@@ -152,5 +162,9 @@ __devm_iio_backend_get_from_fwnode_lookup(struct device *dev,
 
 int devm_iio_backend_register(struct device *dev,
 			      const struct iio_backend_ops *ops, void *priv);
-
+ssize_t iio_backend_debugfs_print_chan_status(struct iio_backend *back,
+					      unsigned int chan, char *buf,
+					      size_t len);
+void iio_backend_debugfs_add(struct iio_backend *back,
+			     struct iio_dev *indio_dev);
 #endif

-- 
2.45.2