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From: Stephen Boyd <stephen.boyd@linaro.org>
Date: Wed, 29 Jun 2016 18:04:54 -0700
Message-ID: <CAJOFmgwBWUL9wYmzNgXqidGQbEPNYj-qYZGdNjidJ2Utswm3Gw@mail.gmail.com>
Subject: Re: [PATCH] extcon: Add support for qcom SPMI PMIC USB id detection hardware
To: Chanwoo Choi <cw00.choi@samsung.com>, Rob Herring <robh+dt@kernel.org>
Cc: Chanwoo Choi <cwchoi00@gmail.com>, linux-arm-msm@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Roger Quadros <rogerq@ti.com>
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On 29 June 2016 at 17:35, Chanwoo Choi <cw00.choi@samsung.com> wrote:
> On 2016년 06월 30일 03:48, Stephen Boyd wrote:
>> Quoting Chanwoo Choi (2016-06-28 23:25:57)
>>> On 2016년 06월 29일 06:59, Stephen Boyd wrote:
>>>> Quoting Chanwoo Choi (2016-06-28 05:06:48)
>>>>> 2016-06-28 4:11 GMT+09:00 Stephen Boyd <stephen.boyd@linaro.org>:
>>>>>> Quoting Chanwoo Choi (2016-06-26 04:20:43)
>>>>>>> 2016-06-26 14:56 GMT+09:00 Stephen Boyd <stephen.boyd@linaro.org>:
>>>>>>>> +PROPERTIES
>>>>>>>> +
>>>>>>>> +- compatible:
>>>>>>>> +    Usage: required
>>>>>>>> +    Value type: <string>
>>>>>>>> +    Definition: Should contain "qcom,pm8941-misc";
>>>>>>>> +
>>>>>>>> +- reg:
>>>>>>>> +    Usage: required
>>>>>>>> +    Value type: <u32>
>>>>>>>> +    Definition: Should contain the offset to the misc address space
>>>>>>>
>>>>>>> 'reg' property is used on extcon-qcom-spmi-misc.c?
>>>>>>> I think that you don't need to include this property.
>>>>>>
>>>>>> No it isn't used in the driver right now, but there is a register offset
>>>>>> for this module and there are registers that can be read/written in this
>>>>>> module. I'd like to keep it as required so we can easily read the
>>>>>> registers in the future if needed.
>>>>>
>>>>> OK.
>>>>> But, If you want to remain the reg property, you should add the code to get
>>>>> the register offset by using OF functions. This patch don't include the OF
>>>>> function to handle it.
>>>>>
>>>>
>>>> Sorry I don't follow the argument. I've put the reg property here for
>>>> future proofing so that the binding doesn't have to change in backwards
>>>> incompatible ways in the future if we do need to get the property later.
>>>
>>> I don't mention that 'reg' property should be removed.
>>
>> Ok good. We need to keep reg property as this device is on a bus that
>> uses reg property for addressing.
>>
>>> Just if you want to remain it, you should add some codes as following:
>>> For exmaple,
>>> - of_get_address() to get the address information from device-tree.
>>>
>>> If documentation include the some properties, you should add the handling code
>>> in device driver. When you add the code to get the offset from device-tree,
>>> it doesn't influence the some behavior in the future.
>>
>> Sorry I don't understand that argument. We can put properties into
>> bindings and not use them in drivers if there isn't any immediate need
>> to use them.
>>
>> From what I can tell you're suggesting we call of_get_address() in the
>> driver and then do nothing with the value of the property? Is that just
>> to check that the node is compliant with the binding and actually has a
>> reg property? We don't add code in the kernel to check dts compliance,
>> so I'm not inclined to do anything more here.
>
> I don't agree.
>
> When he DT binding document include the 'reg' property.
> But, the device driver don't include any code to handle the 'reg' property
> (just to get the offset). It is obviously wrong.
>
> It is just basic principle to write the Device-tree binding document.
>
> Other developer who don' know the history about 'reg' property
> would be embarrassed. Why don't extcon driver include the code to
> handle the 'reg' property? There is no method to explain it.
>

Perhaps Rob can explain why having a reg property is required for a
bus that has #address-cells=<1> even though the device driver isn't
using the reg property.