Message-ID: <8b79b662-931f-4634-9389-6602d353d67a@kernel.org>
Date: Mon, 22 Dec 2025 15:22:55 +0100
From: Hans de Goede <hansg@...nel.org>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: Bryan O'Donoghue <bod.linux@...w.ie>, jerome.debretagne@...il.com,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Johannes Berg <johannes@...solutions.net>,
 Lorenzo Bianconi <lorenzo@...nel.org>,
 Maximilian Luz <luzmaximilian@...il.com>,
 Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 Jeff Johnson <jjohnson@...nel.org>, linux-arm-msm@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-wireless@...r.kernel.org, platform-driver-x86@...r.kernel.org,
 ath12k@...ts.infradead.org, Jeff Johnson <jeff.johnson@....qualcomm.com>,
 Dale Whinham <daleyo@...il.com>
Subject: Re: [PATCH v5 2/7] dt-bindings: wireless: ieee80211: Add
 disable-rfkill property

Hi,

On 22-Dec-25 14:41, Manivannan Sadhasivam wrote:
> On Mon, Dec 22, 2025 at 01:41:48PM +0100, Hans de Goede wrote:
>> Hi Mani,
>>
>> On 22-Dec-25 12:45, Manivannan Sadhasivam wrote:
>>> On Mon, Dec 22, 2025 at 11:23:18AM +0100, Hans de Goede wrote:
>>>> +Cc Mani
>>>>
>>>> Hi,
>>>>
>>>> On 20-Dec-25 07:04, Bryan O'Donoghue wrote:
>>>>> On 20/12/2025 00:21, Jérôme de Bretagne via B4 Relay wrote:
>>>>>> From: Jérôme de Bretagne <jerome.debretagne@...il.com>
>>>>>>
>>>>>> For some devices, Wi-Fi is entirely hard blocked by default making
>>>>>> the Wi-Fi radio unusable, except if rfkill is disabled as expected
>>>>>> on those models.
>>>>>>
>>>>>> Commit c6a7c0b09d5f ("wifi: ath12k: Add Support for enabling or
>>>>>> disabling specific features based on ACPI bitflag") added a way to
>>>>>> support features set via ACPI, including the DISABLE_RFKILL bit.
>>>>>>
>>>>>> Add a disable-rfkill property to expose the DISABLE_RFKILL bit
>>>>>> equivalent for devices described by a Devicetree instead of ACPI.
>>>>>>
>>>>>> Signed-off-by: Jérôme de Bretagne <jerome.debretagne@...il.com>
>>>>>> ---
>>>>>>   Documentation/devicetree/bindings/net/wireless/ieee80211.yaml | 6 ++++++
>>>>>>   1 file changed, 6 insertions(+)
>>>>>>
>>>>>> diff --git a/Documentation/devicetree/bindings/net/wireless/ieee80211.yaml b/Documentation/devicetree/bindings/net/wireless/ieee80211.yaml
>>>>>> index d89f7a3f88a71d45d6f4ab2ae909eae09cbcaf9a..c10a4675640be947cd0b5eaec2c7ff367fd93945 100644
>>>>>> --- a/Documentation/devicetree/bindings/net/wireless/ieee80211.yaml
>>>>>> +++ b/Documentation/devicetree/bindings/net/wireless/ieee80211.yaml
>>>>>> @@ -29,6 +29,12 @@ properties:
>>>>>>         different 5 GHz subbands. Using them incorrectly could not work or
>>>>>>         decrease performance noticeably
>>>>>>
>>>>>> +  disable-rfkill:
>>>>>> +    type: boolean
>>>>>> +    description:
>>>>>> +      Disable rfkill for some devices on which Wi-Fi would be entirely hard
>>>>>> +      blocked by default otherwise
>>>>>> +
>>>>>>   additionalProperties: true
>>>>>>
>>>>>>   examples:
>>>>>>
>>>>>> -- 
>>>>>> 2.47.3
>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>> Is this really a hardware description though ?
>>>>
>>>> I would say yes it is. The wifi chip has an rfkill input pin and
>>>> things will be broken when that pin is hardwired to a fixed value
>>>> rather then being actually connected to a GPIO from say
>>>> the embedded controller.
>>>>
>>>
>>> IIUC, even if the M.2 slot has the W_DISABLE1# signal routed from the host,
>>> the device won't make use of it as there is no physical connection. So you want
>>> the WLAN driver to change the state through SW?
>>>
>>>> So I think that we would need here is not a disable-rfkill property
>>>> but some way to indicate in the DT-node that the rfkill input pin
>>>> is not connected and thus should be ignored.
>>>>
>>>> This (the rfkill input pin being not-connected) IMHO very much
>>>> is hw-description.
>>>>
>>>
>>> Though we can argue this way, I would prefer to handle it in the driver. For
>>> example, with my M.2 series, we will end up describing the M.2 slot:
>>>
>>> 	connector {
>>> 		compatible = "pcie-m2-e-connector";
>>> 		w-disable1-gpios = <&tlmm 117 GPIO_ACTIVE_LOW>;
>>> 		...
>>> 		ports {
>>> 			...
>>> 			endpoint@0 {
>>> 				reg = <0>;
>>> 				remote-endpoint = <&pcie4_port0_ep>;
>>> 			};
>>> 		};
>>> 	};
>>>
>>> Then if we use a DT property to convey the RFKILL pin state of the device, we
>>> would need to describe the endpoint device in DT and hardcode the state:
>>>
>>> 	&pcie4_port0 {
>>> 		...
>>> 		port {
>>> 			pcie4_port0_ep: endpoint {
>>> 				remote-endpoint = <&m2_e_pcie_ep>;
>>> 				disable-rfkill;
>>> 			};
>>> 		};
>>> 	};
>>>
>>> So this will essentially make the M.2 device non-swappable unless you change the
>>> DT since you've how hardcoded the device property in the binding. This is
>>> something I try to avoid to make the M.2 slot really swappable.
>>>
>>> For this reason, I would prefer to handle the RFKILL state in the WLAN driver
>>> using the device specific compatible. This will be problematic only if multiple
>>> cards of the same Device ID have different RFKILL state and the devices are not
>>> distinguishable even with sub IDs.
>>
>> I think we're miscommunicating here. I'm not talking about the card having
>> a broken rfkill implementation, I'm talking about the M.2 slot on the mainboard
>> having e.g. W_DISABLE1# hardwired in such a way that cards would interpret it as
>> having to always disable their wifi radio which is very similar to what is
>> happening on the surface device. Except that on the Surface there is no M.2 slot,
>> the wifi is just soldered onto the mainboard I believe.
>>
> 
> Ah, sorry for the confusion. I did misinterpret what you said.
> 
>> Based on experience I'm pretty sure we will encounter M.2 slots which such
>> a hardwired W_DISABLE1# signal sooner rather then later.
>>
> 
> But it makes no sense IMO. Vendors will usually connect unimplemented W_DISABL1#
> GPIOs to a pull-up resistor so that the radios are operational all the time. I
> don't see how they would expect a WLAN or any device with a radio to be
> connected to the slot if they hardwire the pin to low.

Pins which are considered "unused" are also often hardwired
to ground. If the m.2 slot is tested with a wifi-module where
the W_DISABLE1# signal is not used on the wifi-module I can
easily see this happen. I've seen a lot crazier / buggy stuff
happen.

> Are you sure that on the surface the pin is actually hardwired to low and not
> connected to a GPIO that drivers the signal low?

I don't know what is the exact problem on the Surface. I just
expect to see this more often, we've certainly seen lots of
issues like this on x86 laptops. Things end up looking like
the hard rfkill is activated all the time (and we often don't know
if this is a fw issue, or an actually hardwired problem).

Just an example from the top of my head the Broadcom windows
drivers use different BT fw files for the same wifi/bt combo
chip depending on the vend:prod id pair. One of the things which
is different is that some fw files invert the BT rfkill signal
because it is wired wrong (or there is an EC fw bug) and this
is then worked around in the bt fw.

As we see a growing proliferation of arm64 laptops I fully
expect all the fun from having a gazillion different designs
with a time to market rush behind them result in similar issues
on arm64.

Note I'm not saying we must tackle this today, we can wait
till we see the first case in the real world I guess.

I just thought that based on my experience this is more or
less bound to happen, we could comeup with a solution for
this now and then this solution could also nicely serve
the Surface case which started this thread.

But we can also delay tackling this and come up with some
bespoke solution for the Surface case, like as suggested
maybe a special compatible string ?

> It is just hard to believe that board designers can do a blunder like this.

Heh, you won't believe all the crap happening on cheap
x86 devices.

Regards,

Hans

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