linux-kernel - Re: [PATCH v4 3/6] Documentation: DT: Document twl4030-madc-battery bindings

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Message-Id: <844740CD-C95B-4411-A2C8-4906F58DBEE8@goldelico.com>
Date:	Wed, 11 Mar 2015 17:16:34 +0100
From:	"Dr. H. Nikolaus Schaller" <hns@...delico.com>
To:	Tony Lindgren <tony@...mide.com>
Cc:	Marek Belisko <marek@...delico.com>,
	Benoit Cousson <bcousson@...libre.com>,
	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, linux-omap@...r.kernel.org,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH v4 3/6] Documentation: DT: Document twl4030-madc-battery bindings

Hi,

Am 11.03.2015 um 16:24 schrieb Tony Lindgren <tony@...mide.com>:

> Hi,
> 
> * Marek Belisko <marek@...delico.com> [150310 14:28]:
>> Signed-off-by: Marek Belisko <marek@...delico.com>
>> ---
>> .../bindings/power_supply/twl4030_madc_battery.txt | 43 ++++++++++++++++++++++
>> 1 file changed, 43 insertions(+)
>> create mode 100644 Documentation/devicetree/bindings/power_supply/twl4030_madc_battery.txt
>> 
>> diff --git a/Documentation/devicetree/bindings/power_supply/twl4030_madc_battery.txt b/Documentation/devicetree/bindings/power_supply/twl4030_madc_battery.txt
>> new file mode 100644
>> index 0000000..d3dd9d8
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/power_supply/twl4030_madc_battery.txt
>> @@ -0,0 +1,43 @@
>> +twl4030_madc_battery
>> +
>> +Required properties:
>> + - compatible : "ti,twl4030-madc-battery"
>> + - capacity-uah : battery capacity in uAh
>> + - ti,volt-to-capacity-charging-map : list of voltage(mV):level(%) values
>> +	for charging calibration (see example)
>> + - ti,volt-to-capacity-discharging-map : list of voltage(mV):level(%) values
>> +	for discharging calibration (see example)
>> + - io-channels: Should contain IIO channel specifiers
>> +	for each element in io-channel-names.
>> +- io-channel-names: Should contain the following values:
>> + * "temp" - The ADC channel for temperature reading
>> + * "ichg" - The ADC channel for battery charging status
>> + * "vbat" - The ADC channel to measure the battery voltage
>> +
>> +Example:
>> +	madc-battery {
>> +		compatible = "ti,twl4030-madc-battery";
>> +		capacity-uah = <1200000>;
>> +		ti,volt-to-capacity-charging-map = <4200 100>,
>> +					        <4100 75>,
>> +					        <4000 55>,
>> +					        <3900 25>,
>> +					        <3800 5>,
>> +					        <3700 2>,
>> +					        <3600 1>,
>> +					        <3300 0>;
>> +
>> +		ti,volt-to-capacity-discharging-map = <4200 100>
>> +						   <4100 95>,
>> +						   <4000 70>,
>> +						   <3800 50>,
>> +						   <3700 10>,
>> +						   <3600 5>,
>> +						   <3300 0>;
>> +		io-channels = <&twl_madc 1>,
>> +	                      <&twl_madc 10>,
>> +			      <&twl_madc 12>;
>> +		io-channel-names = "temp",
>> +		                   "ichg",
>> +		                   "vbat";
>> +	};
> 
> Rather than just making platform_data into device tree properties..
> 
> Can't you hide the these custom properties behind the compatible flag?
> 
> You can initialize that data in the driver based on the compatible
> flag and the match data.
> 
> This makes sense if you can group things to similar configurations.

Maybe I have not completely understood your proposal.

Do you mean to go back to have big parameter tables for each device/battery
combination in the driver code and the compatible flag (e.g. compatible = “board17”)
chooses the right data set for the charging map and channels?

I thought this is what the DT was introduced for - to have the same driver 
code but adapt to different boards depending on hardware variations.

And batteries have very different characteristics and vary between devices…

The charging maps are depending on the battery type connected to the twl4030
and which madc channel is which value is also a little hardware dependent
(although the twl4030 doesn’t give much choice).

And moving this information into the driver for each board that uses it
would blow up the code.

BR,
Nikolaus

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