linux-kernel - Re: [PATCH] extcon: Add support for qcom SPMI PMIC USB id detection hardware

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Date:	Wed, 29 Jun 2016 15:25:57 +0900
From:	Chanwoo Choi <cw00.choi@...sung.com>
To:	Stephen Boyd <stephen.boyd@...aro.org>,
	Chanwoo Choi <cwchoi00@...il.com>
Cc:	linux-arm-msm@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Roger Quadros <rogerq@...com>
Subject: Re: [PATCH] extcon: Add support for qcom SPMI PMIC USB id detection
 hardware

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@...aro.org>:
>>> Quoting Chanwoo Choi (2016-06-26 04:20:43)
>>>> 2016-06-26 14:56 GMT+09:00 Stephen Boyd <stephen.boyd@...aro.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.
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.

Thanks,
Chanwoo Choi