From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: devicetree@vger.kernel.org, linux-pwm@vger.kernel.org,
Shawn Guo <shawnguo@kernel.org>,
Sascha Hauer <s.hauer@pengutronix.de>,
linux-kernel@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
Thierry Reding <thierry.reding@gmail.com>,
NXP Linux Team <linux-imx@nxp.com>,
Pengutronix Kernel Team <kernel@pengutronix.de>,
Fabio Estevam <festevam@gmail.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 5/6] pwm: mxs: avoid a division in mxs_pwm_apply()
Date: Fri, 4 Oct 2019 16:08:34 +0200 [thread overview]
Message-ID: <20191004140834.4idddyohf52ha4ao@pengutronix.de> (raw)
In-Reply-To: <20191004133207.6663-6-linux@rasmusvillemoes.dk>
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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next prev parent reply other threads:[~2019-10-04 14:08 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-04 13:32 [PATCH v2 0/6] pwm: mxs: add support for setting polarity via DT Rasmus Villemoes
2019-10-04 13:32 ` [PATCH v2 1/6] pwm: mxs: implement ->apply Rasmus Villemoes
2019-10-04 14:18 ` Uwe Kleine-König
2019-10-04 13:32 ` [PATCH v2 2/6] pwm: mxs: remove legacy methods Rasmus Villemoes
2019-10-04 14:19 ` Uwe Kleine-König
2019-10-04 13:32 ` [PATCH v2 3/6] pwm: mxs: add support for inverse polarity Rasmus Villemoes
2019-10-04 14:20 ` Uwe Kleine-König
2019-10-04 13:32 ` [PATCH v2 4/6] dt-bindings: pwm: mxs-pwm: Increase #pwm-cells Rasmus Villemoes
2019-10-04 19:22 ` Uwe Kleine-König
2019-10-04 13:32 ` [PATCH v2 5/6] pwm: mxs: avoid a division in mxs_pwm_apply() Rasmus Villemoes
2019-10-04 14:08 ` Uwe Kleine-König [this message]
2020-01-08 12:41 ` [PATCH v2 0/6] pwm: mxs: add support for setting polarity via DT Thierry Reding
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