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

[Matti Vaittinen]

On 31/03/2025 10:37, Andy Shevchenko wrote:
> On Sun, Mar 30, 2025 at 05:04:36PM +0100, Jonathan Cameron wrote:
> > On Mon, 17 Mar 2025 13:24:07 +0200
> > Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
> > > On 16/03/2025 13:02, Jonathan Cameron wrote:
> > > > On Thu, 13 Mar 2025 09:19:03 +0200
> > > > Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
>
> ...
>
> > > > > +	return (data->alarm_monitored[chan->channel] & BIT(dir));
> > > >
> > > > Drop the outer brackets as not adding anything.
> > >
> > > I just noticed that the integer returned from here is directly provided
> > > to the user-space. I don't know the history, but it feels a bit off to
> > > me. I mean, I would expect the read from sysfs file "*_en" to return '1'
> > > or '0' - not 0x04.
> > >
> > > Oh well, I suppose it's too late to change this in the IIO core - but
> > > I'll do:
> > > 	return !!(data->alarm_monitored[chan->channel] & BIT(dir));
> >
> > Agreed it should be returning 1 or 0.
> >
> > This stuff is a little bit messy.  I'd not be against that ABI
> > cleanup if we squashed the values to 0,1 in the core as a follow up.
> >
> > I doubt anyone relies on getting 0x4 as that would be very driver
> > specific userspace code!
>
> FWIW, the time this discussion was held, I looked at the code and it seems
> we have such drivers. I doubt we can change it without potential breakage of
> (some) user space tools.

Thanks for the check, and for sharing the results Andy.

I was considering this for a while but eventually I didn't want to take 
a chance of breaking things. I have a feeling that majority of 
application writers, who happen to be writing something using a specific 
sensor, would just make their code to match what-ever they see kernel 
retuning via sysfs.

I know younger me would in the early 2000s. If I got a board where I was 
able to read values from sysfs, I would have just written the code which 
matches whatever I saw in sysfs when testing out things. I would have 
tried reading the file and then making my application to expect exactly 
the value "0x4" - assuming other values may have some other, unknown to 
me, meaning. I wouldn't have gone after a documentation, much less to 
send a question or a patch upstream :)

So, I wouldn't be surprized if someone else had done just this same, and 
they might be upset if we break their app(s).

Yours,
	-- Matti