Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <db76b0f9-ead4-4900-648c-45b8bd7b9355@linaro.org>
Date:   Thu, 17 Nov 2022 18:04:01 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.4.2
Subject: Re: [PATCH 1/2] dt-bindings: iio: magnetometer: add ti tmag5273
 documentation file
Content-Language: en-US
To:     Michael Riesch <michael.riesch@wolfvision.net>,
        Gerald Loacker <gerald.loacker@wolfvision.net>,
        Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Cc:     linux-iio@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, Jonathan Cameron <jic23@kernel.org>,
        Lars-Peter Clausen <lars@metafoo.de>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Nikita Yushchenko <nikita.yoush@cogentembedded.com>,
        Jakob Hauser <jahau@rocketmail.com>
References: <20221115073718.2377311-1-gerald.loacker@wolfvision.net>
 <20221115073718.2377311-2-gerald.loacker@wolfvision.net>
 <20221115174355.00004a01@Huawei.com>
 <f52dcb6d-30ec-3d49-7e28-9761462d4799@wolfvision.net>
 <8c2da24c-ae10-40c9-bb3e-b300975a86d7@linaro.org>
 <467929c1-b405-507b-033d-bdc7abce703f@wolfvision.net>
From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <467929c1-b405-507b-033d-bdc7abce703f@wolfvision.net>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 17/11/2022 18:01, Michael Riesch wrote:
> Hi Krzysztof,
> 
> On 11/17/22 17:17, Krzysztof Kozlowski wrote:
>> On 17/11/2022 17:12, Gerald Loacker wrote:
>>>>
>>>>> +
>>>>> +  compatible:
>>>>> +    const: ti,tmag5273
>>>>> +
>>>>> +  reg:
>>>>> +    maxItems: 1
>>>>> +
>>>>> +  "#io-channel-cells":
>>>>> +    const: 1
>>>>> +
>>>>> +  ti,angle-enable:
>>>>> +    description:
>>>>> +      Enables angle measurement in the selected plane.
>>>>> +      0 = OFF
>>>>> +      1 = X-Y (default)
>>>>> +      2 = Y-Z
>>>>> +      3 = X-Z
>>>>
>>>> This feels like something we should be configuring at runtime rather that
>>>> DT, or is it driven by board design or similar?
>>>>
>>>
>>> We use this sensor for a zoom wheel application, there is an EVM from TI
>>> for this as well. So this is for setting the mounting position of the wheel.
>>
>> That's ok, but does not explain why choice of angle measurement should
>> be a property of the hardware. I could imagine configuring device to
>> measure sometimes X-Y and sometimes X-Z, depending on the use case. Use
>> case can change runtime.
> 
> If I may chime in here: in our use case the angle channel is used
> directly as an input to adc-joystick, so that the combination of the two
> is an input device. We feel that in this scenario this angle measurement
> setting *has* to be a hardware property because the correct function of
> the input device depends on the correct choice of the angle property
> (which does not change during runtime, of course).
> 
> If we were to create a different input device in which the magnetometer
> was tilted by 90° (for example), then the angle property could be easily
> changed in the device tree. The user space, on the other hand, couldn't
> possibly know the correct angle property.
> 
> That said, I agree that there may be use cases in which the angle
> property should be changed during runtime. Would it be acceptable to
> create an IIO property that is initialized by the device tree property?
> (Please note that the implementation of the IIO property may not be in
> our scope, though)

It's fine. Thanks for the explanations. For runtime-configurable setups
this still can be changed via some other interface.

Best regards,
Krzysztof