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

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Message-ID: <5b23d077d8882d6b2a2e66817b1b6bcebc6bb5a2.camel@baylibre.com>
Date: Mon, 17 Nov 2025 20:23:35 +0100
From: Francesco Lavra <flavra@...libre.com>
To: Andy Shevchenko <andriy.shevchenko@...el.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, 2025-10-30 at 15:56 +0200, Andy Shevchenko wrote:
> 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).

These are u8 variables, so we can't use the bitmap API. And I don't
understand the reason for using hweight(), given that the !! operators
would still be needed.

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