linux-kernel - Re: [PATCH] hwmon: (ads1015) Add devicetree documentation

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Date:	Thu, 3 Mar 2011 14:25:49 +0100
From:	Wolfram Sang <w.sang@...gutronix.de>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	Dirk Eibach <eibach@...ys.de>, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, rdunlap@...otime.net,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [PATCH] hwmon: (ads1015) Add devicetree documentation

> > Hmm, device tree bindings should be OS-neutral, sysfs is not.
> 
> Why do we document this in the Linux kernel tree then?

To describe which bindings Linux supports.

> > with the active channels. Then again, what is the drawback of exporting
> > all channels?
> 
> Performance and user-friendliness. libsensors-based applications will
> read all available attributes by default, and each reading takes time.
> Letting the platform declare how the inputs are used allows for a sane
> output for "sensors" and other similar tools out of the box, without
> the user having to tinker with ignore statements in configuration files
> to discard the nonsensical values.

OK, that's fine I'd say.

> > Is there another hwmon-driver doing so (couldn't find one)?
> 
> If "doing so" means "letting the user define how the ADC inputs are
> used", then yes, the pcf8591 driver does something similar, except that
> it uses a module parameter for the setting, for historical reasons.
> Platform-provided, per-device data is better in my opinion.

OK. The thing is you can't map platform_data 1:1 to bindings, because
most are very specific to the Linux-driver. Do you think something like
"active-channels" would be sufficent for those other hwmon devices, too?
(I still do not like "exported-channels", because there is no need to
export the channels for the OS. The devicetree is primarily a hardware
description language) Or maybe we go specific and say "ads1015,channel1
= 1"? Maybe somebody knows of a similar chips as a reference?

Regards,

   Wolfram

-- 
Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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