[PATCH v4 07/10] iio: adc: ti-ads7924: Respect device tree config

[Matti Vaittinen]

On 26/02/2025 02:09, David Lechner wrote:
> On 2/24/25 12:34 PM, Matti Vaittinen wrote:
>> The ti-ads7924 driver ignores the device-tree ADC channel specification
>> and always exposes all 4 channels to users whether they are present in
>> the device-tree or not. Additionally, the "reg" values in the channel
>> nodes are ignored, although an error is printed if they are out of range.
>>
>> Register only the channels described in the device-tree, and use the reg
>> property as a channel ID.
>>
>> Signed-off-by: Matti Vaittinen <mazziesaccount at gmail.com>
>>
>> ---
>> Revision history:
>> v3 => v4:
>>   - Adapt to 'drop diff-channel support' changes to ADC-helpers
>>   - select ADC helpers in the Kconfig
>> v2 => v3: New patch
>>
>> Please note that this is potentially breaking existing users if they
>> have wrong values in the device-tree. I believe the device-tree should
>> ideally be respected, and if it says device X has only one channel, then
>> we should believe it and not register 4. Well, we don't live in the
>> ideal world, so even though I believe this is TheRightThingToDo - it may
>> cause havoc because correct device-tree has not been required from the
>> day 1. So, please review and test and apply at your own risk :)
> 
> The DT bindings on this one are a little weird. Usually, if we don't
> use any extra properties from adc.yaml, we leave out the channels. In
> this case it does seem kind of like the original intention was to work
> like you are suggesting, but hard to say since the driver wasn't actually
> implemented that way. I would be more inclined to actually not make the
> breaking change here and instead relax the bindings to make channel nodes
> optional and just have the driver ignore the channel nodes by dropping
> the ads7924_get_channels_config() function completely. This would make
> the driver simpler instead of more complex like this patch does.

I have no strong opinion on this. I see this driver says 'Supported' in 
MAINTAINERS. Maybe Hugo is able to provide some insight?

>> As a side note, this might warrant a fixes tag but the adc-helper -stuff
>> is hardly worth to be backported... (And I've already exceeded my time
>> budget with this series - hence I'll leave crafting backportable fix to
>> TI people ;) )
>>
>> This has only been compile tested! All testing is highly appreciated.
>> ---
> 
> ...
> 
>> -static int ads7924_get_channels_config(struct device *dev)
>> +static int ads7924_get_channels_config(struct iio_dev *indio_dev,
>> +				       struct device *dev)
> 
> Could get dev from indio_dev->dev.parent and keep only one parameter
> to this function.
> 
>>   {
>> -	struct fwnode_handle *node;
>> -	int num_channels = 0;
>> +	struct iio_chan_spec *chan_array;
>> +	int num_channels = 0, i;
> 
> Don't need initialization here.
> 
>> +	static const char * const datasheet_names[] = {
>> +		"AIN0", "AIN1", "AIN2", "AIN3"
>> +	};

Thanks for the review David! I do agree with the comments to the code.

Yours,
	-- Matti