| Message ID | 20191004133207.6663-6-linux@rasmusvillemoes.dk |
|---|---|
| State | Accepted |
| Headers | show |
| Series | pwm: mxs: add support for setting polarity via DT | expand |
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
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 }; struct mxs_pwm_chip { @@ -71,7 +71,7 @@ static int mxs_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm, rate = clk_get_rate(mxs->clk); while (1) { - c = rate / cdiv[div]; + c = rate >> cdiv_shift[div]; c = c * state->period; do_div(c, 1000000000); if (c < PERIOD_PERIOD_MAX)
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(-)