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

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Message-ID: <20251031094336.6f352b4f@pumpkin>
Date: Fri, 31 Oct 2025 09:43:36 +0000
From: David Laight <david.laight.linux@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.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, 31 Oct 2025 08:45:00 +0100
Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> const_ilog2() was a workaround of some sparse issue, which was
> never appeared in the C functions. Replace it with ilog2().
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  drivers/iio/common/scmi_sensors/scmi_iio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/common/scmi_sensors/scmi_iio.c b/drivers/iio/common/scmi_sensors/scmi_iio.c
> index 39c61c47022a..b40c6d6442e6 100644
> --- a/drivers/iio/common/scmi_sensors/scmi_iio.c
> +++ b/drivers/iio/common/scmi_sensors/scmi_iio.c
> @@ -69,7 +69,7 @@ static int scmi_iio_sensor_update_cb(struct notifier_block *nb,
>  		 *  Converting the timestamp to nanoseconds below.
>  		 */
>  		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 ?
Mathematically log2(x)/log2(10) is log10(x) - which would be 9.
The code does seem to be 'in luck' though.
NSEC_PER_SEC is 10^9 or 0x3b9aca00, so ilog2(NSEC_PER_SEC) is 29.
ilog2(10) is 3, and 29/3 is 9.

Do the same for 10^10 and you get 11.

	David

>  		if (tstamp_scale < 0) {
>  			do_div(time, int_pow(10, abs(tstamp_scale)));
>  			time_ns = time;