Re: [PATCH v3 2/2] iio: adc: ad7173: add AD7173 driver

From: Jonathan Cameron <jic23@kernel.org>
To: Ceclan Dumitru-Ioan <mitrutzceclan@gmail.com>
Cc: linus.walleij@linaro.org, brgl@bgdev.pl, andy@kernel.org,
	linux-gpio@vger.kernel.org,
	"Lars-Peter Clausen" <lars@metafoo.de>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Krzysztof Kozlowski" <krzysztof.kozlowski+dt@linaro.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	"Michael Walle" <michael@walle.cc>,
	"Andy Shevchenko" <andy.shevchenko@gmail.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"ChiaEn Wu" <chiaen_wu@richtek.com>,
	"Niklas Schnelle" <schnelle@linux.ibm.com>,
	"Leonard Göhrs" <l.goehrs@pengutronix.de>,
	"Mike Looijmans" <mike.looijmans@topic.nl>,
	"Haibo Chen" <haibo.chen@nxp.com>,
	"Hugo Villeneuve" <hvilleneuve@dimonoff.com>,
	"Ceclan Dumitru" <dumitru.ceclan@analog.com>,
	linux-iio@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 2/2] iio: adc: ad7173: add AD7173 driver
Date: Tue, 10 Oct 2023 11:26:21 +0100	[thread overview]
Message-ID: <20231010112621.0b371e74@jic23-huawei> (raw)
In-Reply-To: <07afa29c-bfef-72dc-d471-f72dfcebe342@gmail.com>

> 
> >> +		chan[chan_index].differential = fwnode_property_read_bool(child, "bipolar");  
> > 
> > bipolar doesn't normally == differential. 
> > You can have unipolar differential (just that you can't get a negative answer)
> > Perhaps just a terminology thing?
> >  
> 
> This device supports only differential channels. Here, the differential flag is used to show
> if bipolar coding should be used.

I'm confused - you are setting differential in the iio_chan_spec with this.
That affects the sysfs naming and a bunch of other stuff - not merely
the bipolar nature of the channel.

> 
> 
> >> +	st->info = device_get_match_data(dev);
> >> +	if (!st->info)
> >> +		return -ENODEV;  
> > This works for the cases of DT and ACPI but not for anyone just
> > using the spi_device_id table. 
> > There is spi_device_get_match_data() to cover all options.
> >   
> I could not find the spi_device_get_match_data() function in the repo.
> It appears however as a suggestion from Andy Shevchenko in a thread:
> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2382960.html
>  Is this it? 

ah. I got the name wrong.
spi_get_device_match_data()

https://elixir.bootlin.com/linux/v6.6-rc5/source/drivers/spi/spi.c#L364