* [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2()
@ 2025-10-31 7:45 Andy Shevchenko
2025-10-31 9:43 ` David Laight
0 siblings, 1 reply; 7+ messages in thread
From: Andy Shevchenko @ 2025-10-31 7:45 UTC (permalink / raw)
To: Jonathan Cameron, Andy Shevchenko, linux-iio, linux-kernel
Cc: Jyoti Bhayana, Jonathan Cameron, David Lechner, Nuno Sá,
Andy Shevchenko
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@linux.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);
if (tstamp_scale < 0) {
do_div(time, int_pow(10, abs(tstamp_scale)));
time_ns = time;
--
2.50.1
^ permalink raw reply related [flat|nested] 7+ messages in thread* Re: [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2()
2025-10-31 7:45 [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2() Andy Shevchenko
@ 2025-10-31 9:43 ` David Laight
2025-10-31 9:54 ` Andy Shevchenko
0 siblings, 1 reply; 7+ messages in thread
From: David Laight @ 2025-10-31 9:43 UTC (permalink / raw)
To: Andy Shevchenko
Cc: Jonathan Cameron, linux-iio, linux-kernel, Jyoti Bhayana,
Jonathan Cameron, David Lechner, Nuno Sá, Andy Shevchenko
On Fri, 31 Oct 2025 08:45:00 +0100
Andy Shevchenko <andriy.shevchenko@linux.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@linux.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;
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2()
2025-10-31 9:43 ` David Laight
@ 2025-10-31 9:54 ` Andy Shevchenko
2025-10-31 12:45 ` David Laight
0 siblings, 1 reply; 7+ messages in thread
From: Andy Shevchenko @ 2025-10-31 9:54 UTC (permalink / raw)
To: David Laight
Cc: Jonathan Cameron, linux-iio, linux-kernel, Jyoti Bhayana,
Jonathan Cameron, David Lechner, Nuno Sá, Andy Shevchenko
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@linux.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 :-) But we have intlog10(), I completely forgot
about it.
> 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.
That code looks like working by luck entirely, TBH. I just took the scope of
the patch to start dropping const_ilog2() usages.
--
With Best Regards,
Andy Shevchenko
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2()
2025-10-31 9:54 ` Andy Shevchenko
@ 2025-10-31 12:45 ` David Laight
2025-10-31 12:51 ` Andy Shevchenko
0 siblings, 1 reply; 7+ messages in thread
From: David Laight @ 2025-10-31 12:45 UTC (permalink / raw)
To: Andy Shevchenko
Cc: Jonathan Cameron, linux-iio, linux-kernel, Jyoti Bhayana,
Jonathan Cameron, David Lechner, Nuno Sá, Andy Shevchenko
On Fri, 31 Oct 2025 11:54:30 +0200
Andy Shevchenko <andriy.shevchenko@linux.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@linux.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.)
>
> > 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.
>
> That code looks like working by luck entirely, TBH. I just took the scope of
> the patch to start dropping const_ilog2() usages.
Something always crawls out of the woodwork...
David
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2()
2025-10-31 12:45 ` David Laight
@ 2025-10-31 12:51 ` Andy Shevchenko
2025-10-31 16:13 ` David Laight
0 siblings, 1 reply; 7+ messages in thread
From: Andy Shevchenko @ 2025-10-31 12:51 UTC (permalink / raw)
To: David Laight
Cc: Jonathan Cameron, linux-iio, linux-kernel, Jyoti Bhayana,
Jonathan Cameron, David Lechner, Nuno Sá, Andy Shevchenko
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@linux.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@linux.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
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2()
2025-10-31 12:51 ` Andy Shevchenko
@ 2025-10-31 16:13 ` David Laight
2025-11-03 8:30 ` Andy Shevchenko
0 siblings, 1 reply; 7+ messages in thread
From: David Laight @ 2025-10-31 16:13 UTC (permalink / raw)
To: Andy Shevchenko
Cc: Jonathan Cameron, linux-iio, linux-kernel, Jyoti Bhayana,
Jonathan Cameron, David Lechner, Nuno Sá, Andy Shevchenko
On Fri, 31 Oct 2025 14:51:57 +0200
Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
> 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@linux.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@linux.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?
Not sure I'd want to get cpp to generate a high-precision log.
It if definitely doable, but will be a mind-blowing mess.
(and I'm not sure how many MB the expanded line would be).
An ilog10() would be easier (probably looking like const_ilog2()).
But for this code just use '+ 9' and add a suitable comment :-)
David
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2()
2025-10-31 16:13 ` David Laight
@ 2025-11-03 8:30 ` Andy Shevchenko
0 siblings, 0 replies; 7+ messages in thread
From: Andy Shevchenko @ 2025-11-03 8:30 UTC (permalink / raw)
To: David Laight
Cc: Jonathan Cameron, linux-iio, linux-kernel, Jyoti Bhayana,
Jonathan Cameron, David Lechner, Nuno Sá, Andy Shevchenko
On Fri, Oct 31, 2025 at 04:13:31PM +0000, David Laight wrote:
> On Fri, 31 Oct 2025 14:51:57 +0200
> Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
> > On Fri, Oct 31, 2025 at 12:45:30PM +0000, David Laight wrote:
...
> > Do you have an idea how to improve that?
>
> Not sure I'd want to get cpp to generate a high-precision log.
> It if definitely doable, but will be a mind-blowing mess.
> (and I'm not sure how many MB the expanded line would be).
> An ilog10() would be easier (probably looking like const_ilog2()).
>
> But for this code just use '+ 9' and add a suitable comment :-)
v2 is sent: 20251103082937.4081863-1-andriy.shevchenko@linux.intel.com
--
With Best Regards,
Andy Shevchenko
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2025-11-03 8:30 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-10-31 7:45 [PATCH v1 1/1] iio: common: scmi_sensors: Replace const_ilog2() with ilog2() Andy Shevchenko
2025-10-31 9:43 ` David Laight
2025-10-31 9:54 ` Andy Shevchenko
2025-10-31 12:45 ` David Laight
2025-10-31 12:51 ` Andy Shevchenko
2025-10-31 16:13 ` David Laight
2025-11-03 8:30 ` Andy Shevchenko
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox