linux-kernel - Re: [PATCH 0/2] iio: Add support for TI ADS1X18 ADCs

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Message-Id: <DEERGRDZ0TM4.NZ6R9JWCSQPL@gmail.com>
Date: Fri, 21 Nov 2025 18:28:10 -0500
From: "Kurt Borja" <kuurtb@...il.com>
To: "David Lechner" <dlechner@...libre.com>, "Kurt Borja"
 <kuurtb@...il.com>, "Jonathan Cameron" <jic23@...nel.org>, "Rob Herring"
 <robh@...nel.org>, "Krzysztof Kozlowski" <krzk+dt@...nel.org>, "Conor
 Dooley" <conor+dt@...nel.org>, "Tobias Sperling"
 <tobias.sperling@...ting.com>
Cc: Nuno Sá <nuno.sa@...log.com>, "Andy Shevchenko"
 <andy@...nel.org>, <linux-iio@...r.kernel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Jonathan
 Cameron" <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH 0/2] iio: Add support for TI ADS1X18 ADCs

Hi David,

On Fri Nov 21, 2025 at 5:32 PM -05, David Lechner wrote:
> On 11/21/25 11:16 AM, Kurt Borja wrote:
>> Hi,
>> 
>> This series adds a new driver for TI ADS1X18 SPI devices.
>> 
>> This is my first time contributing to the IIO subsystem and making
>> dt-bindings documentation, so (don't) go easy on me :p.
>
> I actually had these parts on my radar, so happy to help you out.
> Unfortunately, I don't have the hardware for testing though.
>
> The first thing I was going to do was check the existing drivers
> to make sure that there isn't one already that has a compatible
> register layout. I have a feeling we won't find one, but would be
> good to mention that in the cover to justify adding a new driver.

The closest driver I could find was the ti-ads1015 I2C driver. It has
the same register map and similar specs. Although I think we can adapt
it to be "compatible", I chose to do a different driver for a few
reasons:

  - ads1015 and compatible devices have a separate DRDY interrupt line.

  - The ti-ads1015 driver doesn't support the DRDY interrupt (sleeps
    until data is ready and it doesn't have an iio_trigger).

  - To correctly handle the DOUT/DRDY line we need to manually control
    the spi_bus_lock. And we do it differently based on which IIO device
    mode we are operating on, so it would be difficult to stuff this
    logic into regmap_bus callbacks alone.

  - IMO the end result of merging these drivers would be too messy.

This is just my opinion though, so let me know what you think. If do
agree I will add some of this points in the patch changelog!

>
> There are a couple of similar TI ADCs on the mailing list right
> now, but they are IMHO just slightly too different to share a
> driver, but would be good to look at just to make things are
> consistent on a high level.

Yes, the other two TI ADCs, ADS1120 and ADS131M02 are very different
devices.

>
>> 
>> As explained in Patch 2 changelog, the DRDY interrupt line is shared
>> with the MOSI pin. This awkward quirk is also found on some Analog
>> Devices sigma-delta SPI ADCs, so the interrupt and trigger design is
>> inspired by those.
>
> Yup, that seems to be the best way we know how to handle this.


-- 
 ~ Kurt