On 12/28/21 18:13, Guenter Roeck wrote:

On 12/27/21 2:42 PM, Cosmin Tanislav wrote:

quoted

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.

Patch looks good afaics. I don't want to apply it now (ie for 5.17),
though, because it is getting close and we don't have a use case.
If you have one in mind, I'd suggest to submit it together with
this patch, or we'll have to wait until there is a user.

Guenter

As I mentioned previously I have a local patch on top of the ADT7X10
refactor that uses this. I tested your modifications to my patchset on
the ADT7420 part and it seems to work just fine. I can push it on top of
either this patch or that patchset, your choice.

quoted

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);
  };
  /**