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

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Message-ID: <615beafaf18edfcf441d62a81c847f7624eef13c.camel@rong.moe>
Date: Wed, 05 Nov 2025 04:27:14 +0800
From: Rong Zhang <i@...g.moe>
To: Armin Wolf <W_Armin@....de>, 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

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@....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 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;