Re: [PATCH v6 5/9] platform/x86: dell-ddv: Use new buffer-based WMI API

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Wed, 10 Jun 2026, Armin Wolf wrote:

> Use the new buffer-based WMI API to also support ACPI firmware
> implementations that do not use ACPI intergers/strings/packages
> for exchanging data.
> 
> Signed-off-by: Armin Wolf <W_Armin@gmx.de>
> ---
>  drivers/platform/x86/dell/dell-wmi-ddv.c | 179 +++++++++++------------
>  1 file changed, 85 insertions(+), 94 deletions(-)
> 
> diff --git a/drivers/platform/x86/dell/dell-wmi-ddv.c b/drivers/platform/x86/dell/dell-wmi-ddv.c
> index 62e3d060f038..736d9b1fdcfb 100644
> --- a/drivers/platform/x86/dell/dell-wmi-ddv.c
> +++ b/drivers/platform/x86/dell/dell-wmi-ddv.c
> @@ -7,8 +7,9 @@
>  
>  #define pr_format(fmt) KBUILD_MODNAME ": " fmt
>  
> -#include <linux/acpi.h>
>  #include <linux/bitfield.h>
> +#include <linux/cleanup.h>
> +#include <linux/compiler_attributes.h>
>  #include <linux/debugfs.h>
>  #include <linux/device.h>
>  #include <linux/device/driver.h>
> @@ -99,6 +100,11 @@ enum dell_ddv_method {
>  	DELL_DDV_THERMAL_SENSOR_INFORMATION	= 0x22,
>  };
>  
> +struct dell_wmi_buffer {
> +	__le32 raw_size;
> +	u8 raw_data[];
> +} __packed;
> +
>  struct fan_sensor_entry {
>  	u8 type;
>  	__le16 rpm;
> @@ -126,7 +132,7 @@ struct dell_wmi_ddv_sensors {
>  	bool active;
>  	struct mutex lock;	/* protect caching */
>  	unsigned long timestamp;
> -	union acpi_object *obj;
> +	struct dell_wmi_buffer *buffer;
>  	u64 entries;
>  };
>  
> @@ -158,105 +164,96 @@ static const char * const fan_dock_labels[] = {
>  	"Docking Chipset Fan",
>  };
>  
> -static int dell_wmi_ddv_query_type(struct wmi_device *wdev, enum dell_ddv_method method, u32 arg,
> -				   union acpi_object **result, acpi_object_type type)
> +static int dell_wmi_ddv_query(struct wmi_device *wdev, enum dell_ddv_method method, u32 arg,
> +			      struct wmi_buffer *output, size_t min_size)
>  {
> -	struct acpi_buffer out = { ACPI_ALLOCATE_BUFFER, NULL };
> -	const struct acpi_buffer in = {
> -		.length = sizeof(arg),
> -		.pointer = &arg,
> +	__le32 arg2 = cpu_to_le32(arg);
> +	const struct wmi_buffer input = {
> +		.length = sizeof(arg2),
> +		.data = &arg2,
>  	};
> -	union acpi_object *obj;
> -	acpi_status ret;
> -
> -	ret = wmidev_evaluate_method(wdev, 0x0, method, &in, &out);
> -	if (ACPI_FAILURE(ret))
> -		return -EIO;
> -
> -	obj = out.pointer;
> -	if (!obj)
> -		return -ENODATA;
> -
> -	if (obj->type != type) {
> -		kfree(obj);
> -		return -ENOMSG;
> -	}
> -
> -	*result = obj;
>  
> -	return 0;
> +	return wmidev_invoke_method(wdev, 0x0, method, &input, output, min_size);
>  }
>  
>  static int dell_wmi_ddv_query_integer(struct wmi_device *wdev, enum dell_ddv_method method,
>  				      u32 arg, u32 *res)
>  {
> -	union acpi_object *obj;
> +	struct wmi_buffer output;
>  	int ret;
>  
> -	ret = dell_wmi_ddv_query_type(wdev, method, arg, &obj, ACPI_TYPE_INTEGER);
> +	ret = dell_wmi_ddv_query(wdev, method, arg, &output, sizeof(__le32));
>  	if (ret < 0)
>  		return ret;
>  
> -	if (obj->integer.value <= U32_MAX)
> -		*res = (u32)obj->integer.value;
> -	else
> -		ret = -ERANGE;
> +	__le32 *argr __free(kfree) = output.data;
>  
> -	kfree(obj);
> +	*res = le32_to_cpu(*argr);
>  
> -	return ret;
> +	return 0;
>  }
>  
>  static int dell_wmi_ddv_query_buffer(struct wmi_device *wdev, enum dell_ddv_method method,
> -				     u32 arg, union acpi_object **result)
> +				     u32 arg, struct dell_wmi_buffer **result)
>  {
> -	union acpi_object *obj;
> -	u64 buffer_size;
> +	struct dell_wmi_buffer *buffer;
> +	struct wmi_buffer output;
> +	size_t buffer_size;
>  	int ret;
>  
> -	ret = dell_wmi_ddv_query_type(wdev, method, arg, &obj, ACPI_TYPE_PACKAGE);
> +	ret = dell_wmi_ddv_query(wdev, method, arg, &output, sizeof(*buffer));
>  	if (ret < 0)
>  		return ret;
>  
> -	if (obj->package.count != 2 ||
> -	    obj->package.elements[0].type != ACPI_TYPE_INTEGER ||
> -	    obj->package.elements[1].type != ACPI_TYPE_BUFFER) {
> -		ret = -ENOMSG;
> -
> -		goto err_free;
> -	}
> -
> -	buffer_size = obj->package.elements[0].integer.value;
> -
> -	if (!buffer_size) {
> +	buffer = output.data;
> +	if (!le32_to_cpu(buffer->raw_size)) {
>  		ret = -ENODATA;
>  
>  		goto err_free;
>  	}
>  
> -	if (buffer_size > obj->package.elements[1].buffer.length) {
> +	buffer_size = struct_size(buffer, raw_data, le32_to_cpu(buffer->raw_size));
> +	if (buffer_size > output.length) {
>  		dev_warn(&wdev->dev,
> -			 FW_WARN "WMI buffer size (%llu) exceeds ACPI buffer size (%d)\n",
> -			 buffer_size, obj->package.elements[1].buffer.length);
> +			 FW_WARN "Dell WMI buffer size (%zu) exceeds WMI buffer size (%zu)\n",
> +			 buffer_size, output.length);
>  		ret = -EMSGSIZE;
>  
>  		goto err_free;
>  	}
>  
> -	*result = obj;
> +	*result = buffer;

This could use __free() and no_free_ptr() to simplify the code flow.

>  
>  	return 0;
>  
>  err_free:
> -	kfree(obj);
> +	kfree(output.data);
>  
>  	return ret;
>  }
>  
> -static int dell_wmi_ddv_query_string(struct wmi_device *wdev, enum dell_ddv_method method,
> -				     u32 arg, union acpi_object **result)
> +static ssize_t dell_wmi_ddv_query_string(struct wmi_device *wdev, enum dell_ddv_method method,
> +					 u32 arg, char *buf, size_t length)
>  {
> -	return dell_wmi_ddv_query_type(wdev, method, arg, result, ACPI_TYPE_STRING);
> +	struct wmi_buffer output;
> +	size_t str_size;
> +	int ret;
> +
> +	ret = dell_wmi_ddv_query(wdev, method, arg, &output, sizeof(struct wmi_string));
> +	if (ret < 0)
> +		return ret;
> +
> +	struct wmi_string *str __free(kfree) = output.data;
> +
> +	str_size = sizeof(*str) + le16_to_cpu(str->length);
> +	if (str_size > output.length) {
> +		dev_warn(&wdev->dev,
> +			 FW_WARN "WMI string size (%zu) exceeds WMI buffer size (%zu)\n",
> +			 str_size, output.length);
> +		return -EMSGSIZE;
> +	}
> +
> +	return wmi_string_to_utf8s(str, buf, length);
>  }
>  
>  /*
> @@ -265,28 +262,26 @@ static int dell_wmi_ddv_query_string(struct wmi_device *wdev, enum dell_ddv_meth
>  static int dell_wmi_ddv_update_sensors(struct wmi_device *wdev, enum dell_ddv_method method,
>  				       struct dell_wmi_ddv_sensors *sensors, size_t entry_size)
>  {
> +	struct dell_wmi_buffer *buffer;
>  	u64 buffer_size, rem, entries;
> -	union acpi_object *obj;
> -	u8 *buffer;
>  	int ret;
>  
> -	if (sensors->obj) {
> +	if (sensors->buffer) {
>  		if (time_before(jiffies, sensors->timestamp + HZ))
>  			return 0;
>  
> -		kfree(sensors->obj);
> -		sensors->obj = NULL;
> +		kfree(sensors->buffer);
> +		sensors->buffer = NULL;
>  	}
>  
> -	ret = dell_wmi_ddv_query_buffer(wdev, method, 0, &obj);
> +	ret = dell_wmi_ddv_query_buffer(wdev, method, 0, &buffer);
>  	if (ret < 0)
>  		return ret;
>  
>  	/* buffer format sanity check */
> -	buffer_size = obj->package.elements[0].integer.value;
> -	buffer = obj->package.elements[1].buffer.pointer;
> +	buffer_size = le32_to_cpu(buffer->raw_size);
>  	entries = div64_u64_rem(buffer_size, entry_size, &rem);
> -	if (rem != 1 || buffer[buffer_size - 1] != 0xff) {
> +	if (rem != 1 || buffer->raw_data[buffer_size - 1] != 0xff) {
>  		ret = -ENOMSG;
>  		goto err_free;
>  	}
> @@ -296,14 +291,14 @@ static int dell_wmi_ddv_update_sensors(struct wmi_device *wdev, enum dell_ddv_me
>  		goto err_free;
>  	}
>  
> -	sensors->obj = obj;
> +	sensors->buffer = buffer;
>  	sensors->entries = entries;
>  	sensors->timestamp = jiffies;
>  
>  	return 0;
>  
>  err_free:
> -	kfree(obj);
> +	kfree(buffer);
>  
>  	return ret;
>  }
> @@ -328,7 +323,7 @@ static int dell_wmi_ddv_fan_read_channel(struct dell_wmi_ddv_data *data, u32 att
>  	if (channel >= data->fans.entries)
>  		return -ENXIO;
>  
> -	entry = (struct fan_sensor_entry *)data->fans.obj->package.elements[1].buffer.pointer;
> +	entry = (struct fan_sensor_entry *)data->fans.buffer->raw_data;
>  	switch (attr) {
>  	case hwmon_fan_input:
>  		*val = get_unaligned_le16(&entry[channel].rpm);
> @@ -354,7 +349,7 @@ static int dell_wmi_ddv_temp_read_channel(struct dell_wmi_ddv_data *data, u32 at
>  	if (channel >= data->temps.entries)
>  		return -ENXIO;
>  
> -	entry = (struct thermal_sensor_entry *)data->temps.obj->package.elements[1].buffer.pointer;
> +	entry = (struct thermal_sensor_entry *)data->temps.buffer->raw_data;
>  	switch (attr) {
>  	case hwmon_temp_input:
>  		*val = entry[channel].now * 1000;
> @@ -411,7 +406,7 @@ static int dell_wmi_ddv_fan_read_string(struct dell_wmi_ddv_data *data, int chan
>  	if (channel >= data->fans.entries)
>  		return -ENXIO;
>  
> -	entry = (struct fan_sensor_entry *)data->fans.obj->package.elements[1].buffer.pointer;
> +	entry = (struct fan_sensor_entry *)data->fans.buffer->raw_data;
>  	type = entry[channel].type;
>  	switch (type) {
>  	case 0x00 ... 0x07:
> @@ -442,7 +437,7 @@ static int dell_wmi_ddv_temp_read_string(struct dell_wmi_ddv_data *data, int cha
>  	if (channel >= data->temps.entries)
>  		return -ENXIO;
>  
> -	entry = (struct thermal_sensor_entry *)data->temps.obj->package.elements[1].buffer.pointer;
> +	entry = (struct thermal_sensor_entry *)data->temps.buffer->raw_data;
>  	switch (entry[channel].type) {
>  	case 0x00:
>  		*str = "CPU";
> @@ -553,8 +548,8 @@ static void dell_wmi_ddv_hwmon_cache_invalidate(struct dell_wmi_ddv_sensors *sen
>  		return;
>  
>  	mutex_lock(&sensors->lock);
> -	kfree(sensors->obj);
> -	sensors->obj = NULL;
> +	kfree(sensors->buffer);
> +	sensors->buffer = NULL;
>  	mutex_unlock(&sensors->lock);
>  }
>  
> @@ -564,7 +559,7 @@ static void dell_wmi_ddv_hwmon_cache_destroy(void *data)
>  
>  	sensors->active = false;
>  	mutex_destroy(&sensors->lock);
> -	kfree(sensors->obj);
> +	kfree(sensors->buffer);
>  }
>  
>  static struct hwmon_channel_info *dell_wmi_ddv_channel_init(struct wmi_device *wdev,
> @@ -750,7 +745,7 @@ static void dell_wmi_battery_invalidate(struct dell_wmi_ddv_data *data,
>  static ssize_t eppid_show(struct device *dev, struct device_attribute *attr, char *buf)
>  {
>  	struct dell_wmi_ddv_data *data = container_of(attr, struct dell_wmi_ddv_data, eppid_attr);
> -	union acpi_object *obj;
> +	ssize_t count;
>  	u32 index;
>  	int ret;
>  
> @@ -758,19 +753,19 @@ static ssize_t eppid_show(struct device *dev, struct device_attribute *attr, cha
>  	if (ret < 0)
>  		return ret;
>  
> -	ret = dell_wmi_ddv_query_string(data->wdev, DELL_DDV_BATTERY_EPPID, index, &obj);
> -	if (ret < 0)
> -		return ret;
> -
> -	if (obj->string.length != DELL_EPPID_LENGTH && obj->string.length != DELL_EPPID_EXT_LENGTH)
> -		dev_info_once(&data->wdev->dev, FW_INFO "Suspicious ePPID length (%d)\n",
> -			      obj->string.length);
> +	count = dell_wmi_ddv_query_string(data->wdev, DELL_DDV_BATTERY_EPPID, index, buf,
> +					  PAGE_SIZE);
> +	if (count < 0)
> +		return count;
>  
> -	ret = sysfs_emit(buf, "%s\n", obj->string.pointer);
> +	if (count != DELL_EPPID_LENGTH && count != DELL_EPPID_EXT_LENGTH)
> +		dev_info_once(&data->wdev->dev, FW_INFO "Suspicious ePPID length (%zd)\n", count);
>  
> -	kfree(obj);
> +	ret = sysfs_emit_at(buf, count, "\n");

What's going on with this change? I see it printing nothing but a newline 
character anymore?

--
 i.

> +	if (ret < 0)
> +		return ret;
>  
> -	return ret;
> +	return count + ret;
>  }
>  
>  static int dell_wmi_ddv_get_health(struct dell_wmi_ddv_data *data, u32 index,
> @@ -994,19 +989,15 @@ static int dell_wmi_ddv_buffer_read(struct seq_file *seq, enum dell_ddv_method m
>  {
>  	struct device *dev = seq->private;
>  	struct dell_wmi_ddv_data *data = dev_get_drvdata(dev);
> -	union acpi_object *obj;
> -	u64 size;
> -	u8 *buf;
> +	struct dell_wmi_buffer *buffer;
>  	int ret;
>  
> -	ret = dell_wmi_ddv_query_buffer(data->wdev, method, 0, &obj);
> +	ret = dell_wmi_ddv_query_buffer(data->wdev, method, 0, &buffer);
>  	if (ret < 0)
>  		return ret;
>  
> -	size = obj->package.elements[0].integer.value;
> -	buf = obj->package.elements[1].buffer.pointer;
> -	ret = seq_write(seq, buf, size);
> -	kfree(obj);
> +	ret = seq_write(seq, buffer->raw_data, le32_to_cpu(buffer->raw_size));
> +	kfree(buffer);
>  
>  	return ret;
>  }
>