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@gmx.de>
Link: https://lore.kernel.org/r/f1787927-b655-4321-b9d9-bc12353c72db@gmx.de/
Signed-off-by: Rong Zhang <i@rong.moe>
Reviewed-by: Derek J. Clark <derekjohn.clark@gmail.com>
Tested-by: Derek J. Clark <derekjohn.clark@gmail.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;
 
-		*retval = (u32)ret_obj->integer.value;
+			*retval = *((u32 *)ret_obj->buffer.pointer);
+			return 0;
+		}
+		case ACPI_TYPE_INTEGER:
+			*retval = (u32)ret_obj->integer.value;
+			return 0;
+		default:
+			return -ENXIO;
+		}
 	}
 
 	return 0;
-- 
2.51.0

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@gmx.de>
> Link: https://lore.kernel.org/r/f1787927-b655-4321-b9d9-bc12353c72db@gmx.de/
> Signed-off-by: Rong Zhang <i@rong.moe>
> Reviewed-by: Derek J. Clark <derekjohn.clark@gmail.com>
> Tested-by: Derek J. Clark <derekjohn.clark@gmail.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;

Hi Armin,

On Tue, 2025-11-04 at 21:13 +0100, Armin Wolf wrote:
> 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@gmx.de>
> > Link: https://lore.kernel.org/r/f1787927-b655-4321-b9d9-bc12353c72db@gmx.de/
> > Signed-off-by: Rong Zhang <i@rong.moe>
> > Reviewed-by: Derek J. Clark <derekjohn.clark@gmail.com>
> > Tested-by: Derek J. Clark <derekjohn.clark@gmail.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 for your review and information. Will do in v4.

> Thanks,
> Armin Wolf

Thanks,
Rong

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