linux-kernel - Re: [PATCH v10 8/8] iio: adc: ad4851: add ad485x driver

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Message-ID: <134bd7b9-f659-4010-9c78-48eee1dc901a@baylibre.com>
Date: Sat, 18 Jan 2025 11:09:12 -0600
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Antoniu Miclaus <antoniu.miclaus@...log.com>, robh@...nel.org,
 conor+dt@...nel.org, linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH v10 8/8] iio: adc: ad4851: add ad485x driver

On 1/18/25 10:57 AM, Jonathan Cameron wrote:
> On Fri, 17 Jan 2025 15:45:35 -0600
> David Lechner <dlechner@...libre.com> wrote:
> 
>> On 1/17/25 7:07 AM, Antoniu Miclaus wrote:

...

>>> +		if (fwnode_property_present(child, "diff-channels")) {
>>> +			*channels = ad4851_chan_diff;
>>> +			channels->scan_index = index++;
>>> +			channels->channel = reg;
>>> +			channels->channel2 = reg;  
>>
>> Typically we don't set channel == channel2 for differential channels.
> So i guess this is tripping up on these being dedicated pairs labelled
> +IN1,-IN1 on the datasheet.  The binding documents those as matching
> the diff-channels - hence both channels and reg are the same.
> So maybe best bet is to enforce that in the driver by checking it is
> true.

Are you saying that in_voltage0-voltage0_raw in userspace is OK?

> 
> It is a slightly weird description but only alternative would be to
> invent some more channel numbers for the negative sides which is
> less than ideal.  We could go that way though.
> 
> Some comments alongside a sanity check is probably the best way to
> handle this and no surprise us in the future.
>