Hi Geert-san,
> From: Geert Uytterhoeven, Sent: Tuesday, January 8, 2019 5:22 PM
>
> Hi Shimoda-san,
>
> On Tue, Jan 8, 2019 at 4:31 AM Yoshihiro Shimoda
> <yoshihiro.shimoda.uh@xxxxxxxxxxx> wrote:
> > The rcar_pwm_get_clock_division() has a loop to calculate the divider,
> > but the value of div should be calculatable without a loop. So,
> > this patch improves it.
> >
> > This algorithm is suggested by Uwe Kleine-König and Laurent Pinchart.
> >
> > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
> > ---
> > drivers/pwm/pwm-rcar.c | 16 +++++++---------
> > 1 file changed, 7 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/pwm/pwm-rcar.c b/drivers/pwm/pwm-rcar.c
> > index 6dbb70c..0498a93 100644
> > --- a/drivers/pwm/pwm-rcar.c
> > +++ b/drivers/pwm/pwm-rcar.c
> > @@ -8,6 +8,8 @@
> > #include <linux/clk.h>
> > #include <linux/err.h>
> > #include <linux/io.h>
> > +#include <linux/log2.h>
> > +#include <linux/math64.h>
> > #include <linux/module.h>
> > #include <linux/of.h>
> > #include <linux/platform_device.h>
> > @@ -68,19 +70,15 @@ static void rcar_pwm_update(struct rcar_pwm_chip *rp, u32 mask, u32 data,
> > static int rcar_pwm_get_clock_division(struct rcar_pwm_chip *rp, int period_ns)
> > {
> > unsigned long clk_rate = clk_get_rate(rp->clk);
> > - unsigned long long max; /* max cycle / nanoseconds */
> > - unsigned int div;
> > + u64 div, tmp;
> >
> > if (clk_rate == 0)
> > return -EINVAL;
> >
> > - for (div = 0; div <= RCAR_PWM_MAX_DIVISION; div++) {
> > - max = (unsigned long long)NSEC_PER_SEC * RCAR_PWM_MAX_CYCLE *
> > - (1 << div);
> > - do_div(max, clk_rate);
> > - if (period_ns <= max)
> > - break;
> > - }
> > + div = NSEC_PER_SEC * RCAR_PWM_MAX_CYCLE;
>
> As we have:
>
> #define NSEC_PER_SEC 1000000000L
> #define RCAR_PWM_MAX_CYCLE 1023
>
> NSEC_PER_SEC is 64-bit on arm64, and 32-bit on arm32.
>
> Hence you should use
>
> div = (u64)NSEC_PER_SEC * RCAR_PWM_MAX_CYCLE;
>
> to avoid overflow on arm32.
Thank you for the comment! I'll fix this.
Best regards,
Yoshihiro Shimoda
> > + tmp = (u64)period_ns * clk_rate + div - 1;
> > + tmp = div64_u64(tmp, div);
> > + div = ilog2(tmp - 1) + 1;
> >
> > return (div <= RCAR_PWM_MAX_DIVISION) ? div : -ERANGE;
> > }
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> -- Linus Torvalds
