Hi Uwe,
> Subject: Re: [PATCH v7 2/2] pwm: Add support for RZ/G2L GPT
>
> 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;
>
Round_pow_of_two(n) --> n=0 is not acceptable
Round_pow_of_two(58)--> 64 as per the above formula, it becomes 64 + 1 /2 = 32
Which is very high value.
I am sure since the expected result is log4, we don't get the desired result with
The above equation. Please correct me, if I am wrong.
0
100
10000
1000000
100000000
Cheers,
Biju
