linux-kernel - Re: [PATCH v2 2/2] iio: add driver for the TI DAC8554

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Message-ID: <20141215100213.GA6159@avionic-0071.adnet.avionic-design.de>
Date:	Mon, 15 Dec 2014 11:02:13 +0100
From:	Nikolaus Schulz <nikolaus.schulz@...onic-design.de>
To:	Hartmut Knaack <knaack.h@....de>
Cc:	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Michael Welling <mwelling@...e.org>,
	Philippe Reynes <tremyfr@...oo.fr>,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org,
	Alban Bedel <alban.bedel@...onic-design.de>
Subject: Re: [PATCH v2 2/2] iio: add driver for the TI DAC8554

On Sat, Dec 13, 2014 at 12:18:50PM +0100, Hartmut Knaack wrote:
> Nikolaus Schulz schrieb am 12.12.2014 um 16:58:
> > On Sat, Dec 06, 2014 at 12:36:19PM +0100, Hartmut Knaack wrote:
> >> Nikolaus Schulz schrieb am 24.11.2014 um 20:50:
> >>> The TI DAC8554 is a quad-channel Digital-to-Analog Converter with an SPI
> >>> interface.
[dac8554_probe:]
> >>> +	st->vref_mv =oltage_uv / 1000;
> >> How hard do you want to depend on a voltage regulator? Doing regulator_get_voltage()
> >> could even be called dynamically in _read_raw(), making a real regulator optional.
> > 
> > Hmm. I understand that the DAC voltage input may not be provided by a
> > regulator, but is that a common scenario?  No other DAC driver I looked
> > at handles that case, they all consider it an error if the regulator is
> > absent.
> > 
> I had people in mind, who might want to use such DAC with one of the popular
> embedded boards like Raspberry Pi - people who would just like to "plug and
> play" without the need or ability to build a kernel (or would prefer to go
> with the convenience of a distribution kernel). But since you've put a
> dependency on OF, I don't see a way to use this device with a stock distribution
> kernel anyway.

As long as the kernel supports devicetree, compiling the module and a
new DT blob should be enough to enable support for the DAC8554.

And, as Jonathan has pointed out, if there is no real regulator
providing the input current, a fixed regulator can be added to the DT.

> But I still think that calculating the actual voltage during _read_raw() would
> be a good idea, as there is support for regulators providing different voltages,
> which can be changed during runtime.

Agreed.

-- 
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