Unverified Commit b990a06f authored by Armin Wolf's avatar Armin Wolf Committed by Ilpo Järvinen
Browse files

platform/wmi: Add helper functions for WMI string conversions 



WMI strings are encoded using UTF16-LE characters, forcing WMI drivers
to manually convert them to/from standard UTF8 strings. Add a two
helper functions for those tasks.

Signed-off-by: default avatarArmin Wolf <W_Armin@gmx.de>
Link: https://patch.msgid.link/20260116204116.4030-4-W_Armin@gmx.de


Reviewed-by: default avatarIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
parent 29dfba69

Documentation/driver-api/wmi.rst

+3 −0
Original line number Diff line number Diff line
@@ -16,5 +16,8 @@ which will be bound to compatible WMI devices by the driver core. 
.. kernel-doc:: include/linux/wmi.h

   :internal:



.. kernel-doc:: drivers/platform/wmi/string.c

   :export:



.. kernel-doc:: drivers/platform/wmi/core.c

   :export:

drivers/platform/wmi/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 
menuconfig ACPI_WMI

	tristate "ACPI-WMI support"

	depends on ACPI && X86

	select NLS

	help

	  This option enables support for the ACPI-WMI driver core.

drivers/platform/wmi/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -4,7 +4,7 @@ 
# ACPI WMI core

#



wmi-y			:= core.o marshalling.o

wmi-y			:= core.o marshalling.o string.o

obj-$(CONFIG_ACPI_WMI)	+= wmi.o



# Unit tests

drivers/platform/wmi/string.c

0 → 100644
+92 −0
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// SPDX-License-Identifier: GPL-2.0-or-later

/*

 * WMI string utility functions.

 *

 * Copyright (C) 2025 Armin Wolf <W_Armin@gmx.de>

 */



#include <linux/build_bug.h>

#include <linux/compiler_types.h>

#include <linux/err.h>

#include <linux/export.h>

#include <linux/nls.h>

#include <linux/limits.h>

#include <linux/types.h>

#include <linux/wmi.h>



#include <asm/byteorder.h>



static_assert(sizeof(__le16) == sizeof(wchar_t));



/**

 * wmi_string_to_utf8s - Convert a WMI string into a UTF8 string.

 * @str: WMI string representation

 * @dst: Buffer to fill with UTF8 characters

 * @length: Length of the destination buffer

 *

 * Convert as WMI string into a standard UTF8 string. The conversion will stop

 * once a NUL character is detected or when the buffer is full. Any invalid UTF16

 * characters will be ignored. The resulting UTF8 string will always be NUL-terminated

 * when this function returns successfully.

 *

 * Return: Length of the resulting UTF8 string or negative errno code on failure.

 */

ssize_t wmi_string_to_utf8s(const struct wmi_string *str, u8 *dst, size_t length)

{

	/* Contains the maximum number of UTF16 code points to read */

	int inlen = le16_to_cpu(str->length) / 2;

	int ret;



	if (length < 1)

		return -EINVAL;



	/* We must leave room for the NUL character at the end of the destination buffer */

	ret = utf16s_to_utf8s((__force const wchar_t *)str->chars, inlen, UTF16_LITTLE_ENDIAN, dst,

			      length - 1);

	if (ret < 0)

		return ret;



	dst[ret] = '\0';



	return ret;

}

EXPORT_SYMBOL_GPL(wmi_string_to_utf8s);



/**

 * wmi_string_from_utf8s - Convert a UTF8 string into a WMI string.

 * @str: WMI string representation

 * @max_chars: Maximum number of UTF16 code points to store inside the WMI string

 * @src: UTF8 string to convert

 * @src_length: Length of the source string without any trailing NUL-characters

 *

 * Convert a UTF8 string into a WMI string. The conversion will stop when the WMI string is

 * full. The resulting WMI string will always be NUL-terminated and have its length field set

 * to and appropriate value when this function returns successfully.

 *

 * Return: Number of UTF16 code points inside the WMI string or negative errno code on failure.

 */

ssize_t wmi_string_from_utf8s(struct wmi_string *str, size_t max_chars, const u8 *src,

			      size_t src_length)

{

	size_t str_length;

	int ret;



	if (max_chars < 1)

		return -EINVAL;



	/* We must leave room for the NUL character at the end of the WMI string */

	ret = utf8s_to_utf16s(src, src_length, UTF16_LITTLE_ENDIAN, (__force wchar_t *)str->chars,

			      max_chars - 1);

	if (ret < 0)

		return ret;



	str_length = (ret + 1) * sizeof(u16);

	if (str_length > U16_MAX)

		return -EOVERFLOW;



	str->length = cpu_to_le16(str_length);

	str->chars[ret] = '\0';



	return ret;

}

EXPORT_SYMBOL_GPL(wmi_string_from_utf8s);

include/linux/wmi.h

+5 −0
Original line number Diff line number Diff line
@@ -62,6 +62,11 @@ struct wmi_string { 
	__le16 chars[];

} __packed;



ssize_t wmi_string_to_utf8s(const struct wmi_string *str, u8 *dst, size_t length);



ssize_t wmi_string_from_utf8s(struct wmi_string *str, size_t max_chars, const u8 *src,

			      size_t src_length);



int wmidev_invoke_method(struct wmi_device *wdev, u8 instance, u32 method_id,

			 const struct wmi_buffer *in, struct wmi_buffer *out);