linux-kernel - Re: [PATCH v2] ARM: zynq: Add #io-channel-cells to (x)adc node for iio-hwmon

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Date:   Thu, 16 Mar 2017 22:23:13 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Moritz Fischer <mdf@...nel.org>
Cc:     Michal Simek <michal.simek@...inx.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        Sören Brinkmann <soren.brinkmann@...inx.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Julia Cartwright <julia@...com>
Subject: Re: [PATCH v2] ARM: zynq: Add #io-channel-cells to (x)adc node for
 iio-hwmon

On 03/16/2017 06:54 PM, Moritz Fischer wrote:
> Hi Lars,
> 
> On Thu, Mar 16, 2017 at 9:51 AM, Lars-Peter Clausen <lars@...afoo.de> wrote:
>> On 03/16/2017 05:45 PM, Michal Simek wrote:
>>> On 16.3.2017 17:39, Moritz Fischer wrote:
>>>> On Thu, Mar 16, 2017 at 9:16 AM, Michal Simek <michal.simek@...inx.com> wrote:
>>>>> Hi,
>>>>>
>>>>> On 8.3.2017 21:11, Moritz Fischer wrote:
>>>>>> Fix
>>>>>>
>>>>>> OF: /iio_hwmon: could not get #io-channel-cells for
>>>>>> /amba/adc@...07100
>>>>>> OF: /iio_hwmon: could not get #io-channel-cells for
>>>>>> /amba/adc@...07100
>>>>>> OF: /iio_hwmon: could not get #io-channel-cells for
>>>>>> /amba/adc@...07100
>>>>>>
>>>>>> by adding the #io-channel-cells property.
>>>>>>
>>>>>> Signed-off-by: Moritz Fischer <mdf@...nel.org>
>>>>>> Cc: Michal Simek <michal.simek@...inx.com>
>>>>>> Cc: Sören Brinkmann <soren.brinkmann@...inx.com>
>>>>>> Cc: Julia Cartwright <julia@...com>
>>>>>> Cc: linux-kernel@...r.kernel.org
>>>>>> Cc: devicetree@...r.kernel.org
>>>>>> ---
>>>>>>
>>>>>> Changes from v1:
>>>>>> - fix messed up commit message
>>>>>> ---
>>>>>>  arch/arm/boot/dts/zynq-7000.dtsi | 1 +
>>>>>>  1 file changed, 1 insertion(+)
>>>>>>
>>>>>> diff --git a/arch/arm/boot/dts/zynq-7000.dtsi b/arch/arm/boot/dts/zynq-7000.dtsi
>>>>>> index f3ac9bf..98233a8 100644
>>>>>> --- a/arch/arm/boot/dts/zynq-7000.dtsi
>>>>>> +++ b/arch/arm/boot/dts/zynq-7000.dtsi
>>>>>> @@ -72,6 +72,7 @@
>>>>>>                       interrupts = <0 7 4>;
>>>>>>                       interrupt-parent = <&intc>;
>>>>>>                       clocks = <&clkc 12>;
>>>>>> +                     #io-channel-cells = <1>;
>>>>>>               };
>>>>>>
>>>>>>               can0: can@...08000 {
>>>>>>
>>>>>
>>>>> I think it will be good to the next step too.
>>>>> It means also add iio-hwmon node too.
>>>>>
>>>>> What do you think?
>>>>
>>>> I hadn't put it in there since dts is supposed to describe hw,
>>>> but obviously putting the actual hwmon in there makes it more useful.
>>>
>>> I had one discussion about this with Grant in past and it is common
>>> mistake. It is simplification of purpose of dts.
>>>
>>
>> If the iio-hwmon binding had gone through review it would have been rejected.
>>
>>>>
>>>> I can resubmit with the hwmon node in there.
>>>
>>> If you grep kernel tree you will see that others are using it too.
>>> Also there is accepted binding for that that's why I can't see big
>>> problem with it.
>>
>> Since this is an application specific binding I wouldn't put it in the
>> generic DT include file. It's a bit like adding a gpio-key binding for each
>> of the GPIOs just in case somebody wants to use it.
> 
> So is your suggestion to move the whole thing from .dtsi -> .dts?

The #io-channels-cells can go into the dtsi, that's a sensible thing to do.
The number of cells is part of the binding specification for the XADC and
wont change.

The hwmon bridge on the other hand I wouldn't put into any default
devicetree. In my opinion is should only used if and only if there are
legacy applications on a specific system that need to use the hwmon interface.