[PATCH v2 0/1] Add hwmon debugfs register access

[PATCH v2 0/1] Add hwmon debugfs register access

[Cosmin Tanislav]

V1 -> V2:
 * remove error messages that are reported to userspace
 * remove IS_ERR checks that are already done by called functions
 * unconditionally define hwmon_device_{un,}register_debugfs
 * unconditionally define struct hwmon_device members
 * match hwmon_debugfs_read_reg parameter indentation with
   hwmon_debugfs_write_reg parameter indentation
 * inline hdev in reg_access calls
 * remove useless initialization of val inside hwmon_debugfs_read_reg
 * move checks outside of hwmon_device_register_debugfs
 * debugfs_reg_access -> reg_access
 * lookup device debugfs dentry rather than storing it in
   struct hwmon_device

Cosmin Tanislav (1):
  hwmon: Add debugfs register access

 Documentation/hwmon/hwmon-kernel-api.rst |  9 +++
 drivers/hwmon/hwmon.c                    | 99 ++++++++++++++++++++++++
 include/linux/hwmon.h                    | 12 +++
 3 files changed, 120 insertions(+)

-- 
2.34.1

[PATCH v2 1/1] hwmon: Add debugfs register access

[Cosmin Tanislav]

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

Re: [PATCH v2 1/1] hwmon: Add debugfs register access

[Guenter Roeck]

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

> 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);
>   };
>   
>   /**
> 

Re: [PATCH v2 1/1] hwmon: Add debugfs register access

[Cosmin Tanislav]

On 12/28/21 18:13, Guenter Roeck wrote:
> On 12/27/21 2:42 PM, Cosmin Tanislav wrote:
>> 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.

> 
>> 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);
>>   };
>>   /**
>>
> 

Re: [PATCH v2 1/1] hwmon: Add debugfs register access

[Guenter Roeck]

On Tue, Dec 28, 2021 at 06:51:40PM +0200, Cosmin Tanislav wrote:
> 
> 
> On 12/28/21 18:13, Guenter Roeck wrote:
> > On 12/27/21 2:42 PM, Cosmin Tanislav wrote:
> > > 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.
> 
The adt7x10 patches won't make it into 5.17 either, so all that will
have to wait until 5.18. If I don't get a use case by then I may write
one myself, but that won't happen now because I am about to be away
from my computers for the next two weeks.

Guenter