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Date: Wed, 25 Mar 2026 19:42:27 +0000
From: Jonathan Cameron <jic23@kernel.org>
To: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: Gabriel Rondon <grondon@gmail.com>, David Lechner
 <dlechner@baylibre.com>, Nuno Sa <nuno.sa@analog.com>, Andy Shevchenko
 <andy@kernel.org>, linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iio: adc: ti-ads8688: use read_avail for available
 attributes
Message-ID: <20260325194227.5d112a85@jic23-huawei>
In-Reply-To: <acJ4sPoX_UqorDXS@ashevche-desk.local>
References: <20260323215633.8140-1-grondon@gmail.com>
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On Tue, 24 Mar 2026 13:42:40 +0200
Andy Shevchenko <andriy.shevchenko@intel.com> wrote:

> On Mon, Mar 23, 2026 at 09:56:33PM +0000, Gabriel Rondon wrote:
> > Convert the in_voltage_scale_available and in_voltage_offset_available
> > attributes from legacy IIO_DEVICE_ATTR with custom show functions to the
> > IIO framework's read_avail callback. This uses the framework's built-in
> > support for _available attributes, removing the need for manual sysfs
> > formatting.
> > 
> > Precompute the available scale values at probe time since they depend on
> > the reference voltage which does not change after initialization.  
> 
> ...
> 
> > +static const int ads8688_offset_avail[] = {
> > +	-(1 << (ADS8688_REALBITS - 1)),  
> 
> This is fragile code (however it probably won't be exposed IRL)
> if ADS8688_REALBITS == 32 this is UB in accordance with C standard.
> 
> Also the trick with -BIT(x) is harder to read than simple GENMASK().
> If ADS8688_REALBITS == 1, this becomes -1 (all ones), is it correct?
> 
> > +	0,  

Replying here because the follow up lost too much context.
This is a classic offset for bipolar ADC, which is - half the full
range binary value.  So we won't hit the edge cases, but maybe
expressing it different will be clearer.

-(GENMASK(ADS8688_REALBITS - 1, 0) >> 1) does feel a bit overkill
but -GENMASK(ADS8688_REALBITS - 2, 0) feels under explained (much
like the current).

We 'could' use -(U16MAX >> 1) but that feels very specific to
it being 16 bits.

Maybe just leave this as it already is in the table the value
is copied from.