linux-kernel - Re: [PATCH 2/3] iio: temperature: add max6675 thermocouple converter driver

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Message-ID: <20150803231019.GJ15004@beef>
Date:	Mon, 3 Aug 2015 19:10:19 -0400
From:	Matt Porter <mporter@...sulko.com>
To:	Matt Ranostay <mranostay@...il.com>
Cc:	Linux IIO List <linux-iio@...r.kernel.org>,
	Devicetree List <devicetree@...r.kernel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] iio: temperature: add max6675 thermocouple converter
 driver

On Mon, Aug 03, 2015 at 03:39:00PM -0700, Matt Ranostay Matt Ranostay wrote:
> On Mon, Aug 3, 2015 at 1:56 PM, Matt Porter <mporter@...sulko.com> wrote:

...

> > +static int max6675_probe(struct spi_device *spi)
> > +{
> > +       struct iio_dev *indio_dev;
> > +       struct max6675_state *st;
> > +       int ret = 0;
> > +
> > +       indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
> > +       if (!indio_dev)
> > +               return -ENOMEM;
> > +
> > +       st = iio_priv(indio_dev);
> > +       st->spi = spi;
> > +
> > +       spi->mode = SPI_MODE_1;
> > +       spi->bits_per_word = 16;
> 
> Have this error or display a warning when it doesn't match the passed
> DT binding settings. Otherwise it may get confusing why other SPI
> modes and word sizes don't work.

Ok, good point. The only thing here is that I've specified that spi-cpha
is required in the binding, indicating that Mode 1 will be used. I need
this driver to be instantiated via three methods: ACPI, DT, and "board
file" so for the latter I'm hardcoding in the driver the mode. The
device only works in Mode 1 so this seems sane, it's not configurable.
I don't parse that mode from either DT or ACPI data since it's not
needed. About the only thing I could do is pedantically check for
spi-cpha and if not present complain..but I think it's fine to simply
not parse at all given that we've hardcoded this for the allowed mode.

There's no property for bits_per_word, it's configured on a per-transfer
basis. In this case, this configures the default to do a 16-bit transfer
as required by the device. There is no way to modify this by a client of
this driver.

-Matt
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