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Date: Tue, 28 Dec 2021 08:13:01 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Cosmin Tanislav <demonsingur@...il.com>
Cc: cosmin.tanislav@...log.com, Jean Delvare <jdelvare@...e.com>,
Jonathan Corbet <corbet@....net>, linux-hwmon@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] hwmon: Add debugfs register access
On 12/27/21 2:42 PM, Cosmin Tanislav wrote:
> From: Cosmin Tanislav <cosmin.tanislav@...log.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@...log.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", ®, &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);
> };
>
> /**
>
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