Message-ID: <7420fc7a-4a65-0ff8-adb8-f2e9815fdeba@metafoo.de>
Date:   Mon, 20 Mar 2017 16:34:43 +0100
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Michal Simek <michal.simek@...inx.com>,
        Moritz Fischer <moritz.fischer.private@...il.com>
Cc:     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 03/20/2017 04:33 PM, Michal Simek wrote:
> On 17.3.2017 07:46, Michal Simek wrote:
>> On 16.3.2017 22:20, Lars-Peter Clausen wrote:
>>> On 03/16/2017 07:06 PM, Michal Simek wrote:
>>>> On 16.3.2017 17:51, Lars-Peter Clausen 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.
>>>>
>>>> Isn't it a time to deprecate it?
>>>
>>> Well, it's ABI now and has to stay forever. Deprecating it makes only sense
>>> if there is a replacement, which there is not. The iio-hwmon bridge has its
>>> usecases it's just instantiating it via devicetree which is not so nice.
>>>
>>>>
>>>>>
>>>>>>>
>>>>>>> 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.
>>>>
>>>> psci is system specific too.
>>>>
>>>> IIRC this driver for zynq was written by ADI or with ADI help that's why
>>>> you know much better than I what's the correct configuration.
>>>>
>>>> This targets PS IP which should be present in the hw all the time.
>>>> Not sure if for all configuration but I expect at least the part of it
>>>> is there all them time.
>>>>
>>>> If binding is incorrect then please remove it with removing from all
>>>> dts/dtsi files which have this. The same is for of probe function in the
>>>> driver itself.
>>>> If this is not done then this is just +1 case.
>>>>
>>>> If you still insist that we shouldn't do it then please at least extend
>>>> commit message and put there example how to wire it on zynq.
>>>
>>> There is a IIO driver for the XADC, this driver has a userspace interface
>>> that exposes the measurements provided by the hardware. Using the hwmon
>>> bridge will expose the same information just through a hwmon interface.
>>>
>>> One reason for using the iio-hwmon bridge is because you have a legacy
>>> application that expects the a hwmon interface. But new applications that
>>> want to access the XADC should really use the IIO interface if possible.
>>>
>>> In my opinion instantiating the hwmon bridge by default will only cause
>>> confusion. There are now redundant interfaces and users will wonder what is
>>> the difference between the two. Is it the same data, is it different data?
>>> Which is the preferred interface? Which one is 'better'?
>>
>> IMHO this should be covered by documentation. One paragraph in iio-hwmon
>> binding can have answers for this and it will be very clear what people
>> should use.
> 
> Any comment on this one?

Send a patch? :)

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