Re: [PATCH v7 06/10] iio: adc: Support ROHM BD79124 ADC

[Matti Vaittinen]

On 17/03/2025 09:57, Andy Shevchenko wrote:
> On Mon, Mar 17, 2025 at 09:07:30AM +0200, Matti Vaittinen wrote:
> > On 14/03/2025 16:37, Andy Shevchenko wrote:
> > > On Fri, Mar 14, 2025 at 11:22:37AM +0200, Matti Vaittinen wrote:
>
> ...
>
> > > Okay, it seems I misinterpreted the values you have in regmap configuration,
> > > I was under the impression that regmap is 16-bit data, but it is about address.
> > >
> > > So, we need to know why the heck HW has sparse registers
> >
> > We don't know. And we really don't even need to know it. We can just use
> > this device knowing there are some.
>
> Don't you have a channel to ask HW engineers about this?

Let's just say that ROHM is, while not huge, still rather large company. 
I'm located far away from the HQ, I speak different language and I am 
from very different cultural background. So, while there are some 
channels, it is not always easy, clever of possible to ask (not to 
mention getting answers to) "why this way" - questions :)

> > > for what is supposed
> > > to be sequential. This needs a good comment.
> >
> > I think it is quite usual that devices contain undocumented registers. Not
> > sure having a comment that this device also has some, adds much of value? I
> > suppose I can add a comment that we can't use bulk_write because registers
> > aren't in subsequent addresses - but having just removed bunch of
> > unnecessary comments from the code (as requested), I'm not sure adding this
> > one really improves situation... When one sees separate reads/writes for
> > data spread to multiple registers, he is likely to assume addresses aren't
> > subsequent.
>
>  From HW design perspective it's silly to sparse hi and lo part of
> the semantically same entity. So, either the (undocumented) register
> is also part of the soup, or the registers have different semantics.

Or, the designer has not thought how software would be doing the reads. 
Or, this design has originated from a design done for a very specific 
purpose, which, we don't know of.

> This what needs to be commented in my opinion.

Yours,
	-- Matti