linux-kernel - Re: [PATCH v3 1/6] platform/x86: lenovo-wmi-helpers: Convert returned 4B buffer into u32

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Message-ID: <a0b6d30b-3cba-4760-81dc-099e8fada7c0@gmx.de>
Date: Tue, 4 Nov 2025 21:13:17 +0100
From: Armin Wolf <W_Armin@....de>
To: Rong Zhang <i@...g.moe>, Mark Pearson <mpearson-lenovo@...ebb.ca>,
 "Derek J. Clark" <derekjohn.clark@...il.com>,
 Hans de Goede <hansg@...nel.org>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Guenter Roeck <linux@...ck-us.net>, platform-driver-x86@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org
Subject: Re: [PATCH v3 1/6] platform/x86: lenovo-wmi-helpers: Convert returned
 4B buffer into u32

Am 31.10.25 um 16:51 schrieb Rong Zhang:

> The Windows WMI-ACPI driver converts all ACPI objects into a common
> buffer format, so returning a buffer with four bytes will look like an
> integer for WMI consumers under Windows.
>
> Therefore, some devices may simply implement the corresponding ACPI
> methods to always return a buffer. While lwmi_dev_evaluate_int() expects
> an integer (u32), convert returned 4-byte buffer into u32 to support
> these devices.
>
> Suggested-by: Armin Wolf <W_Armin@....de>
> Link: https://lore.kernel.org/r/f1787927-b655-4321-b9d9-bc12353c72db@gmx.de/
> Signed-off-by: Rong Zhang <i@...g.moe>
> Reviewed-by: Derek J. Clark <derekjohn.clark@...il.com>
> Tested-by: Derek J. Clark <derekjohn.clark@...il.com>
> ---
> Changes in v2:
> - New patch (thanks Armin Wolf)
> ---
>   drivers/platform/x86/lenovo/wmi-helpers.c | 21 ++++++++++++++++++---
>   1 file changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/platform/x86/lenovo/wmi-helpers.c b/drivers/platform/x86/lenovo/wmi-helpers.c
> index f6fef6296251..f3bc92ac505a 100644
> --- a/drivers/platform/x86/lenovo/wmi-helpers.c
> +++ b/drivers/platform/x86/lenovo/wmi-helpers.c
> @@ -59,10 +59,25 @@ int lwmi_dev_evaluate_int(struct wmi_device *wdev, u8 instance, u32 method_id,
>   		if (!ret_obj)
>   			return -ENODATA;
>   
> -		if (ret_obj->type != ACPI_TYPE_INTEGER)
> -			return -ENXIO;
> +		switch (ret_obj->type) {
> +		/*
> +		 * The ACPI method may simply return a 4-byte buffer when a u32
> +		 * integer is expected. This is valid on Windows as its WMI-ACPI
> +		 * driver converts everything to a common buffer.
> +		 */
> +		case ACPI_TYPE_BUFFER: {
> +			if (ret_obj->buffer.length != 4)
> +				return -ENXIO;

The Windows driver also accepts oversized buffers. I suggest that you follow this behavior
for the sake of compatibility.

>   
> -		*retval = (u32)ret_obj->integer.value;
> +			*retval = *((u32 *)ret_obj->buffer.pointer);

The buffer can be unaligned. Better use get_unaligned_le32() from linux/unaligned.h.

Thanks,
Armin Wolf

> +			return 0;
> +		}
> +		case ACPI_TYPE_INTEGER:
> +			*retval = (u32)ret_obj->integer.value;
> +			return 0;
> +		default:
> +			return -ENXIO;
> +		}
>   	}
>   
>   	return 0;