Messages in this thread | | | Date | Fri, 4 Oct 2019 16:08:34 +0200 | From | Uwe Kleine-König <> | Subject | Re: [PATCH v2 5/6] pwm: mxs: avoid a division in mxs_pwm_apply() |
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On Fri, Oct 04, 2019 at 03:32:06PM +0200, Rasmus Villemoes wrote: > Since the divisor is not a compile-time constant (unless gcc somehow > decided to unroll the loop PERIOD_CDIV_MAX times), this does a > somewhat expensive 32/32 division. Replace that with a right shift. > > We still have a 64/32 division just below, but at least in that > case the divisor is compile-time constant. > > Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> --- > drivers/pwm/pwm-mxs.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/pwm/pwm-mxs.c b/drivers/pwm/pwm-mxs.c > index 57562221c439..f2e57fcf8f8b 100644 > --- a/drivers/pwm/pwm-mxs.c > +++ b/drivers/pwm/pwm-mxs.c > @@ -33,8 +33,8 @@ > #define PERIOD_CDIV(div) (((div) & 0x7) << 20) > #define PERIOD_CDIV_MAX 8 > > -static const unsigned int cdiv[PERIOD_CDIV_MAX] = { > - 1, 2, 4, 8, 16, 64, 256, 1024 > +static const u8 cdiv_shift[PERIOD_CDIV_MAX] = { > + 0, 1, 2, 3, 4, 6, 8, 10
One small nitpick: I would like to see this name have a mxs_pwm_ prefix. But even without this change:
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Thanks Uwe
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |
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