Re: [PATCH v9 7/7] platform/x86: lenovo-wmi-other: Add HWMON for fan reporting/tuning

["Kurt Borja" <kuurtb@gmail.com>]

On Fri Jan 16, 2026 at 9:18 AM -05, Rong Zhang wrote:
> Hi Kurt,
>
> On Thu, 2026-01-15 at 14:09 -0500, Kurt Borja wrote:
>> On Thu Jan 15, 2026 at 11:57 AM -05, Rong Zhang wrote:
>> > Hi Kurt,
>> > 
>> > On Thu, 2026-01-15 at 08:58 -0500, Kurt Borja wrote:
>> > > On Thu Jan 15, 2026 at 8:03 AM -05, Rong Zhang wrote:
>> > > > Hi Kurt,
>> > > > 
>> > > > On Wed, 2026-01-14 at 19:16 -0500, Kurt Borja wrote:
>> > > > > Hi Rong,
>> > > > > 
>> > > > > On Wed Jan 14, 2026 at 7:27 AM -05, Rong Zhang wrote:
>> > > > > > Register an HWMON device for fan reporting/tuning according to
>> > > > > > Capability Data 00 (capdata00) and Fan Test Data (capdata_fan) provided
>> > > > > > by lenovo-wmi-capdata. The corresponding HWMON nodes are:
>> > > > > > 
>> > > > > >  - fanX_enable: enable/disable the fan (tunable)
>> > > > > >  - fanX_input: current RPM
>> > > > > >  - fanX_max: maximum RPM
>> > > > > >  - fanX_min: minimum RPM
>> > > > > >  - fanX_target: target RPM (tunable)
>> > > > > > 
>> > > > > > Information from capdata00 and capdata_fan are used to control the
>> > > > > > visibility and constraints of HWMON attributes. Fan info from capdata00
>> > > > > > is collected on bind, while fan info from capdata_fan is collected in a
>> > > > > > callback. Once all fan info is collected, register the HWMON device.
>> > > > > > 
>> > > > > > Signed-off-by: Rong Zhang <i@rong.moe>
>> > > > > > Reviewed-by: Derek J. Clark <derekjohn.clark@gmail.com>
>> > > > > > ---
>> > > > > 
>> > > > > ...
>> > > > > 
>> > > > > > diff --git a/Documentation/wmi/devices/lenovo-wmi-other.rst b/Documentation/wmi/devices/lenovo-wmi-other.rst
>> > > > > > index 821282e07d93c..bd1d733ff286d 100644
>> > > > > > --- a/Documentation/wmi/devices/lenovo-wmi-other.rst
>> > > > > > +++ b/Documentation/wmi/devices/lenovo-wmi-other.rst
>> > > > > > @@ -31,6 +31,8 @@ under the following path:
>> > > > > >  
>> > > > > >    /sys/class/firmware-attributes/lenovo-wmi-other/attributes/<attribute>/
>> > > > > >  
>> > > > > > +Additionally, this driver also exports attributes to HWMON.
>> > > > > > +
>> > > > > >  LENOVO_CAPABILITY_DATA_00
>> > > > > >  -------------------------
>> > > > > >  
>> > > > > > @@ -39,6 +41,11 @@ WMI GUID ``362A3AFE-3D96-4665-8530-96DAD5BB300E``
>> > > > > >  The LENOVO_CAPABILITY_DATA_00 interface provides various information that
>> > > > > >  does not rely on the gamezone thermal mode.
>> > > > > >  
>> > > > > > +The following HWMON attributes are implemented:
>> > > > > > + - fanX_enable: enable/disable the fan (tunable)
>> > > > > 
>> > > > > I was testing this series and I'm a bit confused about fanX_enable.
>> > > > 
>> > > > Thanks for testing!
>> > > 
>> > > Thanks for working on this!
>> > > 
>> > > > 
>> > > > > Judging by this comment and also by taking a quick look at the code, it
>> > > > > looks like writting 0 to this attribute disables the fan.
>> > > > > 
>> > > > > This is however (per hwmon ABI documentation [1]) not how this attribute
>> > > > > should work. IIUC, it is intended for devices which can disable the fan
>> > > > > sensor, not the actual fan.
>> > > > 
>> > > > Hmm, what a confusing name :-/
>> > > > 
>> > > > > I fail to see how this feature is useful and I also find it dangerous
>> > > > > for this to be exposed by default, considering the same could be
>> > > > > achieved with the relaxed module parameter, which at least tells the
>> > > > > user to be careful.
>> > > > 
>> > > > Makes sense. I will remove the attribute and mention such behavior in
>> > > > the module parameter.
>> > > 
>> > > Also, it would be worth to mention that writting 0 to the fanY_target
>> > > attribute is auto mode, right?
>> > 
>> > Ah, yes.
>> > 
>> > > I was testing the fanX_target attribute and it does work as intended,
>> > > i.e. the fan speed changes to the desired speed. However, every time I
>> > > write to this attribute I'm getting -EIO error and it always reads 0.
>> > > 
>> > > For example:
>> > > 
>> > > 	$ echo 3550 | sudo tee fan*_target
>> > > 	3550
>> > > 	tee: fan1_target: Input/output error
>> > > 	tee: fan2_target: Input/output error
>> > > 	$ cat fan*_target
>> > > 	0
>> > > 	0
>> > > 
>> > > But as I said, the fans do reach the desired speed (an approximation of
>> > > it):
>> > > 
>> > > 	$ cat fan*_input
>> > > 	3500
>> > > 	3500
>> > > 
>> > > This is a bit weird, but I haven't look in depth into it. I will find
>> > > some time to do it later. This happens on a 83KY (Legion 7 16IAX1)
>> > > laptop.
>> > 
>> > I'd like to fix it in the next revision. Looking forward to your
>> > progress in debugging :-)
>> > 
>> > It seems to me that the corresponding ACPI method did not return 1 on
>> > success. There should be some clues in the decompiled ASL code. Could
>> > you attach it in your reply? The HWMON implementation was developed
>> > mostly based on my understanding on the decompiled ASL code of my
>> > device. I'd like to check the one of your device as a cross-reference
>> > to see if there are more potential bugs.
>> 
>> Yep, the ACPI method retval is 0 instead of 1.
>
> Given the divergence between your device and mine, I think we could
> just accept both 0 and 1. That should be fine considering that we've
> strictly checked LENOVO_CAPABILITY_DATA_00 and LENOVO_FAN_TEST_DATA
> before exposing fan channels.

Thanks! This fixes the -EIO issue.

>
>> Here is a snippet of what I believe is the fan control stuff on my
>> device (L: 50393):
>> 
>> 
>> 	If ((SFV0 == 0x04030001))
>> 	{
>> 		Local0 = (SFV1 / 0x64)
>> 		^^PC00.LPCB.EC0.LECR (0xD1, One, Local0, 0x02)
>> 		Return (Zero)
>> 	}
>> 
>> 	If ((SFV0 == 0x04030002))
>> 	{
>> 		Local0 = (SFV1 / 0x64)
>> 		^^PC00.LPCB.EC0.LECR (0xD1, 0x02, Local0, 0x02)
>> 		Return (Zero)
>> 	}
>> 
>> 	If ((SFV0 == 0x04030004))
>> 	{
>> 		Local0 = (SFV1 / 0x64)
>> 		^^PC00.LPCB.EC0.LECR (0xD1, 0x03, Local0, 0x02)
>> 		Return (Zero)
>> 	}
>
> On my device, 0x04030001 always returns 1 after writing to EC
> registers. 0x04030002 is a stub and always returns 0. That was the
> reason why I assumed 1 => success and 0 => failure. Here's the
> corresponding code snippet on my device:

I had this exact issue in the alienware-wmi-wmax driver. OEMs tend to be
inconsistent with return values across models.

>
>    If ((DEV1 == 0x04))
>    {
>        If ((FEA1 == 0x03))
>        {
>            Local0 = Buffer (0x06){}
>            Local0 [Zero] = 0x46
>            If ((TYP1 == One))
>            {
>                Local1 = ToInteger (DAT1)
>                If ((Local1 == Zero))

Here auto mode is more explicit too.

>                {
>                    Local0 [One] = 0x84
>                }
>                Else
>                {
>                    MBGS ("Fan1S")
>                    Local0 [One] = 0x85
>                    Divide (Local1, 0x64, Local2, Local1)
>                    Local0 [0x02] = Local1
>                }
>            }
>    
>            If ((TYP1 == 0x02))
>            {
>                MBGS ("Fan2S")
>                Return (Zero)
>            }
>    
>            \_SB.PCI0.LPC0.EC0.ERCD (Local0)
>            Return (One)
>        }
>    
>        If ((FEA1 == 0x04))
>        {
>            MBGS ("wSet FanNoise")
>            DB2H (DAT1)
>            \_SB.FANL = DAT1 /* \_SB_.GZFD.WMAE.DAT1 */
>            Notify (\_TZ.VFAN, 0x80) // Status Change
>        }
>    }
>
>> You can find the full acpidump attached in this email.
>
> Thanks for that.
>
>> Do you have any idea of what 0x04030004 might be?
>
> It's "system fan". See
> https://lore.kernel.org/all/CAFqHKTkOZUfDb8cGbGnVPCS9wNbOBsiyOk_MkZR-2_Za6ZPMng@mail.gmail.com/
>
>> This laptop only has 2
>> fans. FW bug?
>
> Nope, that's not a bug as long as LENOVO_CAPABILITY_DATA_00 or
> LENOVO_FAN_TEST_DATA only indicates the presence of fan 1&2. Lenovo
> usually reuses a lot of ASL code among different SKUs, with some other
> mechanism to gate inapplicable functionalities.
>
> So I quickly glanced at the decompiled ASL code of your device...
>
> Method WQA9 is LENOVO_CAPABILITY_DATA_00, and it only exposes fan 4 on
> specific SKUs (L: 47975):
>
>    If (((GSKU == 0x02) || (GSKU == 0x03)))
>    {
>        Return (Buffer (0x0C)
>        {
>            /* 0000 */  0x04, 0x00, 0x03, 0x04, 0x07, 0x00, 0x00, 0x00,
>            /* 0008 */  0x01, 0x00, 0x00, 0x00
>        })
>    }
>    Else
>    {
>        Return (Buffer (0x0C)
>        {
>            /* 0000 */  0x04, 0x00, 0x03, 0x04, 0x00, 0x00, 0x00, 0x00,
>            /* 0008 */  0x00, 0x00, 0x00, 0x00
>        })
>    }
>
> I assume your device should return the latter buffer, indicating fan 4
> does not exist. That being said, it won't be surprising if the former
> one is returned -- my device's LENOVO_CAPABILITY_DATA_00 indicates the
> presence of fan 1&2 while LENOVO_FAN_TEST_DATA only exposes fan 1.
>
> Method WQAB is LENOVO_FAN_TEST_DATA (L: 48195). It exposes fan 1&2,
> declaring their RPM range to be [1700,5700].
>
>    Return (Buffer (0x1C)
>    {
>        /* 0000 */  0x02, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00,
>        /* 0008 */  0x02, 0x00, 0x00, 0x00, 0x44, 0x16, 0x00, 0x00,
>        /* 0010 */  0x44, 0x16, 0x00, 0x00, 0xA4, 0x06, 0x00, 0x00,
>        /* 0018 */  0xA4, 0x06, 0x00, 0x00
>    })
>
> So these WMI interfaces on your device are implemented mostly well.
> LENOVO_FAN_TEST_DATA is enough to prevent fan 4 from being exposed on
> your device.

Yes, fan 4 is not exposed to user-space so everything is fine here.

Thanks for the detailed explaination! I'll check the structure of those
buffers to understand these drivers better.

>
> Thanks,
> Rong


-- 
Thanks,
 ~ Kurt