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Subject[PATCH v2 1/1] hwmon: Add debugfs register access
Date
From: Cosmin Tanislav <cosmin.tanislav@analog.com>

Similar to IIO, create a device directory inside debugfs
mount point, and create a direct_reg_access file inside
that directory, if debugfs_reg_access callback is defined
inside hwmon_ops.

Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
---
Documentation/hwmon/hwmon-kernel-api.rst | 9 +++
drivers/hwmon/hwmon.c | 97 ++++++++++++++++++++++++
include/linux/hwmon.h | 12 +++
3 files changed, 118 insertions(+)

diff --git a/Documentation/hwmon/hwmon-kernel-api.rst b/Documentation/hwmon/hwmon-kernel-api.rst
index c41eb6108103..d568a0bfa5fb 100644
--- a/Documentation/hwmon/hwmon-kernel-api.rst
+++ b/Documentation/hwmon/hwmon-kernel-api.rst
@@ -136,6 +136,8 @@ The list of hwmon operations is defined as::
u32 attr, int, long *);
int (*write)(struct device *, enum hwmon_sensor_types type,
u32 attr, int, long);
+ int (*reg_access)(struct device *dev, unsigned int reg,
+ unsigned int writeval, unsigned int *readval);
};

It defines the following operations.
@@ -152,6 +154,13 @@ It defines the following operations.
Pointer to a function for writing a value to the chip. This function is
optional, but must be provided if any writeable attributes exist.

+* reg_access:
+ Pointer to a function for writing or reading a register to the chip.
+ This function is optional.
+ WARNING: Drivers implementing this function must block any access that
+ may cause issues such as power loss, board resets, flash corruption or
+ bricking.
+
Each sensor channel is described with struct hwmon_channel_info, which is
defined as follows::

diff --git a/drivers/hwmon/hwmon.c b/drivers/hwmon/hwmon.c
index 3501a3ead4ba..027e5fc33114 100644
--- a/drivers/hwmon/hwmon.c
+++ b/drivers/hwmon/hwmon.c
@@ -10,6 +10,7 @@
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/bitops.h>
+#include <linux/debugfs.h>
#include <linux/device.h>
#include <linux/err.h>
#include <linux/gfp.h>
@@ -35,6 +36,9 @@ struct hwmon_device {
struct list_head tzdata;
struct attribute_group group;
const struct attribute_group **groups;
+ unsigned int cached_reg_addr;
+ char read_buf[20];
+ unsigned int read_buf_len;
};

#define to_hwmon_device(d) container_of(d, struct hwmon_device, dev)
@@ -64,6 +68,90 @@ struct hwmon_thermal_data {
struct thermal_zone_device *tzd;/* thermal zone device */
};

+static struct dentry *hwmon_debugfs_dentry;
+
+static ssize_t hwmon_debugfs_read_reg(struct file *file,
+ char __user *userbuf,
+ size_t count, loff_t *ppos)
+{
+ struct hwmon_device *hwdev = file->private_data;
+ unsigned int val;
+ int ret;
+
+ if (*ppos > 0)
+ return simple_read_from_buffer(userbuf, count, ppos,
+ hwdev->read_buf,
+ hwdev->read_buf_len);
+
+ ret = hwdev->chip->ops->reg_access(&hwdev->dev, hwdev->cached_reg_addr,
+ 0, &val);
+ if (ret)
+ return ret;
+
+ hwdev->read_buf_len = snprintf(hwdev->read_buf, sizeof(hwdev->read_buf),
+ "0x%X\n", val);
+
+ return simple_read_from_buffer(userbuf, count, ppos, hwdev->read_buf,
+ hwdev->read_buf_len);
+}
+
+static ssize_t hwmon_debugfs_write_reg(struct file *file,
+ const char __user *userbuf,
+ size_t count, loff_t *ppos)
+{
+ struct hwmon_device *hwdev = file->private_data;
+ unsigned int reg, val;
+ char buf[80];
+ int ret;
+
+ count = min_t(size_t, count, sizeof(buf) - 1);
+ if (copy_from_user(buf, userbuf, count))
+ return -EFAULT;
+
+ buf[count] = 0;
+
+ ret = sscanf(buf, "%i %i", &reg, &val);
+
+ switch (ret) {
+ case 1:
+ hwdev->cached_reg_addr = reg;
+ break;
+ case 2:
+ hwdev->cached_reg_addr = reg;
+ ret = hwdev->chip->ops->reg_access(&hwdev->dev, reg, val, NULL);
+ if (ret)
+ return ret;
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ return count;
+}
+
+static const struct file_operations hwmon_debugfs_reg_fops = {
+ .open = simple_open,
+ .read = hwmon_debugfs_read_reg,
+ .write = hwmon_debugfs_write_reg,
+};
+
+static void hwmon_device_register_debugfs(struct hwmon_device *hwdev)
+{
+ struct dentry *dir = debugfs_create_dir(dev_name(&hwdev->dev),
+ hwmon_debugfs_dentry);
+
+ debugfs_create_file("direct_reg_access", 0644, dir, hwdev,
+ &hwmon_debugfs_reg_fops);
+}
+
+static void hwmon_device_unregister_debugfs(struct hwmon_device *hwdev)
+{
+ struct dentry *dir = debugfs_lookup(dev_name(&hwdev->dev),
+ hwmon_debugfs_dentry);
+
+ debugfs_remove_recursive(dir);
+}
+
static ssize_t
name_show(struct device *dev, struct device_attribute *attr, char *buf)
{
@@ -114,6 +202,8 @@ static void hwmon_dev_release(struct device *dev)
{
struct hwmon_device *hwdev = to_hwmon_device(dev);

+ hwmon_device_unregister_debugfs(hwdev);
+
if (hwdev->group.attrs)
hwmon_free_attrs(hwdev->group.attrs);
kfree(hwdev->groups);
@@ -817,6 +907,9 @@ __hwmon_device_register(struct device *dev, const char *name, void *drvdata,
}
}

+ if (chip && chip->ops->reg_access)
+ hwmon_device_register_debugfs(hwdev);
+
return hdev;

free_hwmon:
@@ -1062,12 +1155,16 @@ static int __init hwmon_init(void)
pr_err("couldn't register hwmon sysfs class\n");
return err;
}
+
+ hwmon_debugfs_dentry = debugfs_create_dir("hwmon", NULL);
+
return 0;
}

static void __exit hwmon_exit(void)
{
class_unregister(&hwmon_class);
+ debugfs_remove(hwmon_debugfs_dentry);
}

subsys_initcall(hwmon_init);
diff --git a/include/linux/hwmon.h b/include/linux/hwmon.h
index fad1f1df26df..587fb2931ac1 100644
--- a/include/linux/hwmon.h
+++ b/include/linux/hwmon.h
@@ -390,6 +390,16 @@ enum hwmon_intrusion_attributes {
* Channel number
* @val: Value to write
* The function returns 0 on success or a negative error number.
+ * @reg_access:
+ * Callback to read or write register values.
+ * Parameters are:
+ * @dev: Pointer to hardware monitoring device
+ * @reg: Register address to read or write
+ * @writeval:
+ * Value to write to register. 0 when reading.
+ * @readval:
+ * Pointer to value read from register. NULL when writing.
+ * The function returns 0 on success or a negative error number.
*/
struct hwmon_ops {
umode_t (*is_visible)(const void *drvdata, enum hwmon_sensor_types type,
@@ -400,6 +410,8 @@ struct hwmon_ops {
u32 attr, int channel, const char **str);
int (*write)(struct device *dev, enum hwmon_sensor_types type,
u32 attr, int channel, long val);
+ int (*reg_access)(struct device *dev, unsigned int reg,
+ unsigned int writeval, unsigned int *readval);
};

/**
--
2.34.1
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