Hello Biju,
On Thu, Sep 29, 2022 at 05:36:38PM +0000, Biju Das wrote:
> > +static u8 rzg2l_calculate_prescale(struct rzg2l_gpt_chip *rzg2l_gpt,
> > + u64 period_cycles)
> > +{
> > + u32 prescaled_period_cycles;
> > + u8 prescale;
> > +
> > + prescaled_period_cycles = period_cycles >> 32;
> > +
> > + if (prescaled_period_cycles >= 256)
> > + prescale = 5;
> > + else
> > + prescale = (roundup_pow_of_two(prescaled_period_cycles + 1)
> > + 1) / 2;
>
>
> This algorithm won't give desired result.
>
> prescaled_period_cycles Expected result
> 0 ->0
> 1..3 ->1
> 4..15 ->2
> 16..63 ->3
> 64..255 ->4
> 256 > ->5
Oh, indeed, it fails for prescaled_period_cycles ∈ { 0, 3, 15, 63, 255 }.
The correct formula is:
if (prescaled_period_cycles >= 256)
prescale = 5;
else
prescale = (roundup_pow_of_two(prescaled_period_cycles) + 1) / 2;
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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