linux-kernel - Re: [PATCH 1/2] iio: vadc: Qualcomm SPMI PMIC voltage ADC driver

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Date:	Tue, 09 Sep 2014 15:49:45 +0300
From:	Stanimir Varbanov <svarbanov@...sol.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Pawel Moll <pawel.moll@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Kumar Gala <galak@...eaurora.org>,
	Mark Rutland <mark.rutland@....com>,
	Grant Likely <grant.likely@...aro.org>,
	Jonathan Cameron <jic23@...nel.org>,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Hartmut Knaack <knaack.h@....de>,
	Angelo Compagnucci <angelo.compagnucci@...il.com>,
	Doug Anderson <dianders@...omium.org>,
	Fugang Duan <B38611@...escale.com>,
	Johannes Thumshirn <johannes.thumshirn@....de>,
	Jean Delvare <jdelvare@...e.de>,
	Philippe Reynes <tremyfr@...oo.fr>,
	Lee Jones <lee.jones@...aro.org>,
	Josh Cartwright <joshc@...eaurora.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	David Collins <collinsd@...eaurora.org>,
	"Ivan T. Ivanov" <iivanov@...sol.com>
Subject: Re: [PATCH 1/2] iio: vadc: Qualcomm SPMI PMIC voltage ADC driver

On 09/09/2014 01:32 PM, Arnd Bergmann wrote:
> On Monday 08 September 2014 18:30:00 Stanimir Varbanov wrote:
>>>>> These numbers all look hardware specific, so why put macros into the
>>>>> device tree rather than using them directly?
>>>>
>>>> The idea was to use #defines in DT nodes when we need to overwrite the
>>>> adc channel parameters, see example in 2/2 how it will be used.
>>>
>>> I don't understand. The node in the example has
>>>
>>> +               /* Channel node */
>>> +               usb_id_nopull@39 {
>>> +                       qcom,channel = <VADC_LR_MUX10_USB_ID>;
>>> ...
>>> +               };
>>>
>>>
>>> And VADC_LR_MUX10_USB_ID is defined to 0x39.  How is this helping anything?
>>> You just introduce an artificial dependency on the header file, which makes
>>> it a mess to merge the patches or do updates, and anybody who needs to
>>> make updates to this now has to go through the same pain, to update the
>>> dts files, the driver and the binding document in lockstep.
>>>
>>> Why not remove the qcom,channel property completely and use a 'reg'
>>> property with #address-cells=<1>, #size-cells=<0> and put the number
>>> directly in there, with no need for obfuscation macros?
>>
>> OK thanks for the remarks. I will fix this mess.
>>
>> I hope you are expecting to see this:
>>
>> pmic_vadc: vadc@...0 {
>>         #address-cells = <1>;
>>         #size-cells = <0>;
>>         #io-channel-cells = <1>;
>>         io-channel-ranges;
>>
>>         usb_id_nopull@39 {
>>                 reg = <0x39>;
>>         };
>> };
>>
>> and use the vadc channel from usb device node
>>
>> usb {
>>         ...
>>         io-channels = <&pmic_vadc 0x39>;
>>         io-channel-names = "usbidnopull";
>> };
> 
> The ID stuff looks good now, but I had not noticed the
> "io-channel-names" property before. I think you misunderstood
> the purpose of that, because it is very similar to the name of the
> adc provider (usb_id_nopull@39).
> 
> Like anything else that we refer to by name (interrupt, reg,
> clock, regulator, ...), the name used in the client is supposed
> to be a string that identifies what the connection means to the
> client, not what it means to the provider. This string is
> supposed to be defined in the binding of the client device and
> independent of what other hardware block provides it.

yes of course, my fault. Thanks for clarification.

-- 
regards,
Stan
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