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Date: Fri, 23 Feb 2024 18:45:52 +0500
From: Nikita Travkin <nikita@trvn.ru>
To: Rob Herring <robh@kernel.org>
Cc: Sebastian Reichel <sre@kernel.org>, Krzysztof Kozlowski
 <krzysztof.kozlowski+dt@linaro.org>, Conor Dooley <conor+dt@kernel.org>,
 cros-qcom-dts-watchers@chromium.org, Andy Gross <agross@kernel.org>, Bjorn
 Andersson <andersson@kernel.org>, Konrad Dybcio <konrad.dybcio@linaro.org>,
 linux-pm@vger.kernel.org, devicetree@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org
Subject: Re: [PATCH v2 1/3] dt-bindings: power: supply: Add Acer Aspire 1 EC
In-Reply-To: <20240223045227.GA4017491-robh@kernel.org>
References: <20231212-aspire1-ec-v2-0-ca495ea0a7ac@trvn.ru>
 <20231212-aspire1-ec-v2-1-ca495ea0a7ac@trvn.ru>
 <20231214220210.GA988134-robh@kernel.org>
 <207edefe4e8eac9679cd8966d28820cd@trvn.ru>
 <20240223045227.GA4017491-robh@kernel.org>
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Rob Herring писал(а) 23.02.2024 09:52:
> On Fri, Dec 15, 2023 at 10:29:22AM +0500, Nikita Travkin wrote:
>> Rob Herring писал(а) 15.12.2023 03:02:
>> > On Tue, Dec 12, 2023 at 05:49:09PM +0500, Nikita Travkin wrote:
>> >> Add binding for the EC found in the Acer Aspire 1 laptop.
>> >>
>> >> Signed-off-by: Nikita Travkin <nikita@trvn.ru>
>> >> ---
>> >>  .../bindings/power/supply/acer,aspire1-ec.yaml     | 67 ++++++++++++++++++++++
>> >>  1 file changed, 67 insertions(+)
>> >>
>> >> diff --git a/Documentation/devicetree/bindings/power/supply/acer,aspire1-ec.yaml b/Documentation/devicetree/bindings/power/supply/acer,aspire1-ec.yaml
>> >> new file mode 100644
>> >> index 000000000000..1fbf1272a00f
>> >> --- /dev/null
>> >> +++ b/Documentation/devicetree/bindings/power/supply/acer,aspire1-ec.yaml
>> >> @@ -0,0 +1,67 @@
>> >> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> >> +%YAML 1.2
>> >> +---
>> >> +$id: http://devicetree.org/schemas/power/supply/acer,aspire1-ec.yaml#
>> >> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> >> +
>> >> +title: Acer Aspire 1 Embedded Controller
>> >> +
>> >> +maintainers:
>> >> +  - Nikita Travkin <nikita@trvn.ru>
>> >> +
>> >> +description:
>> >> +  The Acer Aspire 1 laptop uses an embedded controller to control battery
>> >> +  and charging as well as to provide a set of misc features such as the
>> >> +  laptop lid status and HPD events for the USB Type-C DP alt mode.
>> >> +
>> >> +properties:
>> >> +  compatible:
>> >> +    const: acer,aspire1-ec
>> >> +
>> >> +  reg:
>> >> +    const: 0x76
>> >> +
>> >> +  interrupts:
>> >> +    maxItems: 1
>> >> +
>> >> +  acer,media-keys-on-top:
>> >> +    description: Configure the keyboard layout to use media features of
>> >> +      the fn row when the fn key is not pressed. The firmware may choose
>> >> +      to add this property when user selects the fn mode in the firmware
>> >> +      setup utility.
>> >> +    type: boolean
>> >
>> > Besides the naming, this isn't really a property of the EC, but really
>> > part of the keyboard layout. It seems you just stuck it here because
>> > this is part of the specific device.
>> >
>>
>> The EC on this device is also a keyboard controller, but the keyboard
>> part has a dedicated i2c bus with hid-over-i2c. Since this is the
>> "management" bus of the same device, I decided that it fits here.
> 
> So there's also a hid-over-i2c DT node? Then why wouldn't you put this 
> there?
> 

Yes indeed, however I wasn't sure of a nice way to make two drivers
interact so I opted to having the prop here instead given I was trying
to reflect "device specific" (in terms of uefi setup -> os code
interaction) property.

>>
>> > It is also hardly a feature unique to this device. I'm typing this from
>> > a device with the exact same thing (M1 Macbook Pro). Actually, all 3
>> > laptops I have in front of me have the same thing. The other 2 have
>> > a Fnlock (Fn+ESC) though.  On the M1, it's just a module param which I
>> > set as persistent. Though I now wonder if the Fnlock could be
>> > implemented on it too. Being able to switch whenever I want would be
>> > nice. That would probably have to be in Linux where as these other
>> > laptops probably implement this in their EC/firmware?
>> >
>> > What I'm getting at is controlling changing this in firmware is not a
>> > great experience and this should all be common.
>> >
>>
>> You may be right, however my goal here is to support the original
>> firmware feature that is lost when we use DT.
>>
>> This is a WoA laptop with UEFI/ACPI and, as usual for "Windows"
>> machines, there is a setting in the firmware setup utility ("bios") to
>> set the fn behavior. But it works by setting an ACPI value, and for
>> Snapdragon devices we can't use that now.
>>
>> Long term I want to have a EFI driver that would automatically
>> detect/load DT and my plan is to handle things like this (and i.e. mac
>> address, different touchpad vendor, etc) there. Thus I'm adding this
>> property already, as an equivalent of that weird acpi bit that original
>> firmware sets.
>>
>> If we only provide a module param, the "intended by OEM" way of setting
>> the fn mode will be broken, and one would need to know how to write a
>> magic special config file to set a kernel module param. I think it's not
>> the best UX. (and just adds to the silly "arm/dt bad, x86/uefi/acpi
>> "just works"" argument many people sadly have)
> 
> But it always works, it is just a question of what is the default mode 
> and I, as a user, want to decide that, not the OEM. And I want to change 
> it at run-time, not reboot into BIOS to change it.
> 
> I wasn't suggesting you do a module param either. That's still specific 
> to the module. Something like a sysfs file would be nice:
> 
> echo 1 >  /sys/class/input/input1/fnlock
> 

I see your point. Having a generic way of switching fnlock, attached to
the correct input device would be great. However as I wasn't sure how
exactly that can be implemented in a generic manner, I opted to just
make sure that at least the user manual for this device still "works".

> 
>> If you think I shouldn't use DT to pass this info, feel free to say so.
>> I will drop this property and see if there is something else I can do
>> to still support this without relying on Linux cooperation.
> 
> Not saying no to being in DT, but if it is, it should be a common 
> property because it is a common thing on all laptops.
> 

Right. Then I think I will drop the property for now and will see if
we can introduce something better and generic later.

Thanks for explaining!
Nikita

> Rob