Re: ADS1018 ADC driver

[Guenter Roeck <linux@roeck-us.net>]

Michael,

On 09/21/2015 06:27 PM, Michael Welling wrote:
> On Mon, Sep 21, 2015 at 06:04:36PM -0700, Guenter Roeck wrote:
>> Hi Michael,
>>
>> On 09/21/2015 03:06 PM, Michael Welling wrote:
>>> I am in the process of starting a new device driver for the ADS1018 ADC.
>>> Before starting I did some research as whether similar drivers exist in the kernel.
>>>
>>> It appears that ADC drivers are in both hwmon and iio/adc. The closest drivers to
>>> the device mentioned are in hwmon.
>>>
>>> Where is the best place for this new ADC driver?
>>
>> Your call. You could add support for the chip to hwmon/ads1015.c, or you could write
>> a new driver in iio/adc. If you do the latter, maybe you can also include support
>> for ads1015 and ads1115, so we can ultimately remove the ads1015 driver from hwmon.
>
> Guenter,
>
> Though the iio route may be more work I have a feeling the
> driver will be better off there. The use of regmap support
> should allow for both the SPI and I2C version to coexist.
>
Sorry, you lost me. There is no correlation between iio/hwmon and regmap.
regmap can be (and is) used with both subsystems. Please clarify.

> I will try my best to implement the driver in a way that
> can cover these other I2C devices mentioned.
>
>>
>>> Shouldn't ADCs all be in the same subsystem?
>>> Has there been any effort to unify or distiguish where drivers should go?
>>>
>> In general, ADCs primarily used for the purpose of ADC measurements would go
>> into iio, and ADCs used primarily for hardware monitoring would go into hwmon.
>>
>> There are no strict rules, though, and this is not always black-and-white.
>> I am sure there are some drivers in hwmon which would be better suited for iio.
>> Primarily that would be the case because the iio subsystem is relatively new,
>> and such drivers did not have a home other than hwmon until a couple of years ago.
>> If you find any drivers in hwmon which you think should be moved, please feel free
>> to do the conversion.
>
> Has anyone considered an alternative implementation for generic ADCs?
>
> I was thinking about an implementation similar to gpiolib whereas ADCs can be
> resources for other drivers.
>
> For instance, ADC lines could be registered to a joystick driver and used to provide
> analog stick or pressure sensitive button. Another example could be registering analog
> lines for an analog accelerometer driver.
>
> Is this a bad idea?
>
I am quite sure that is possible. If it isn't currently supported, it waits for someone
with a use case to implement it.

Guenter