linux-kernel - Re: [PATCH 8/9] iio: imu: st_lsm6dsx: add event configurability on a per axis basis

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Message-ID: <aQNueWesrf_vXO06@smile.fi.intel.com>
Date: Thu, 30 Oct 2025 15:56:09 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Francesco Lavra <flavra@...libre.com>
Cc: Lorenzo Bianconi <lorenzo@...nel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/9] iio: imu: st_lsm6dsx: add event configurability on a
 per axis basis

On Thu, Oct 30, 2025 at 12:23:19PM +0100, Francesco Lavra wrote:
> On Thu, 2025-10-30 at 10:24 +0200, Andy Shevchenko wrote:
> > On Thu, Oct 30, 2025 at 08:27:51AM +0100, Francesco Lavra wrote:

...

> > > +       old_enable = hw->enable_event[event];
> > > +       new_enable = state ? (old_enable | BIT(axis)) : (old_enable &
> > > ~BIT(axis));
> > > +       if (!!old_enable == !!new_enable)
> > 
> > This is an interesting check. So, old_enable and new_enable are _not_
> > booleans, right?
> > So, this means the check test if _any_ of the bit was set and kept set or
> > none were set
> > and non is going to be set. Correct? I think a short comment would be
> > good to have.
> 
> old_enable and new_enable are bit masks, but we are only interested in
> whether any bit is set, to catch the cases where the bit mask goes from
> zero to non-zero and vice versa. Will add a comment.

If it's a true bitmask (assuming unsigned long type) then all this can be done
via bitmap API calls. Otherwise you can also compare a Hamming weights of them
(probably that gives even the same size of the object file, but !! instructions
 will be changed to hweight() calls (still a single assembly instr on modern
 architectures).

-- 
With Best Regards,
Andy Shevchenko