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

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Message-ID: <986c47b4-6093-4e6d-aa4b-8d789e497dbc@baylibre.com>
Date: Fri, 21 Nov 2025 18:02:22 -0600
From: David Lechner <dlechner@...libre.com>
To: 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

On 11/21/25 5:28 PM, Kurt Borja wrote:
> 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).

I don't think this one is a big deal. Ideally, eventually both drivers
would support operating both with and without interrupts.

> 
>   - 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 one I agree with 100%, but for different reasons. ads1015 is I2C
and ads1018 is SPI _and_ regmap is not a good fit for either of these.
Mostly because when reading sample data, we need a custom SPI message
to read the data and write the setup for the next conversion at the
same time. And ads1018 only has 1 register anyway that isn't 100%
identical to the same register in ads1015.

> 
> 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!
> 
In the end, we both have the same conclusion.