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.
> + 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
