linux-kernel - Re: [PATCH v1 1/1] iio: common: scmi_sensors: Replace const

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Message-ID: <aQSw7V7tYjBOtJ7k@smile.fi.intel.com>
Date: Fri, 31 Oct 2025 14:51:57 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: David Laight <david.laight.linux@...il.com>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jyoti Bhayana <jbhayana@...gle.com>,
	Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>
Subject: Re: [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2()
 with ilog2()

On Fri, Oct 31, 2025 at 12:45:30PM +0000, David Laight wrote:
> On Fri, 31 Oct 2025 11:54:30 +0200
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> > On Fri, Oct 31, 2025 at 09:43:36AM +0000, David Laight wrote:
> > > On Fri, 31 Oct 2025 08:45:00 +0100
> > > Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:  

...

> > > >  		tstamp_scale = sensor->sensor_info->tstamp_scale +
> > > > -			       const_ilog2(NSEC_PER_SEC) / const_ilog2(10);
> > > > +			       ilog2(NSEC_PER_SEC) / ilog2(10);  
> > > 
> > > Is that just a strange way of writing 9 ?  
> > 
> > Why? It's correct way of writing log¹⁰(NSEC_PER_SEC), the problem here is that
> > "i" people do not think about :-)
> 
> Even without the "i" the division could easily give 8.999999.
> So you'd be relying on rounding to get the required integral value.
> 
> > But we have intlog10(), I completely forgot about it.
> 
> And it isn't the function the code is looking for.
> (The result is shifted left 24 and it doesn't have an optimisation
> for constants.)

Do you have an idea how to improve that?

-- 
With Best Regards,
Andy Shevchenko