From 8002fbeef1e469b2c397d5cd2940e37b32a17849 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= Date: Sun, 17 Mar 2024 22:52:16 +0100 Subject: [PATCH] pwm: stm32: Calculate prescaler with a division instead of a loop MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Instead of looping over increasing values for the prescaler and testing if it's big enough, calculate the value using a single division. Link: https://lore.kernel.org/r/498a44b313a6c0a84ccddd03cd67aadaaaf7daf2.1710711976.git.u.kleine-koenig@pengutronix.de Signed-off-by: Uwe Kleine-König --- drivers/pwm/pwm-stm32.c | 30 +++++++++++++++++------------- 1 file changed, 17 insertions(+), 13 deletions(-) diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c index ea3d7d9117f2..a2f231d13a9f 100644 --- a/drivers/pwm/pwm-stm32.c +++ b/drivers/pwm/pwm-stm32.c @@ -311,29 +311,33 @@ static int stm32_pwm_capture(struct pwm_chip *chip, struct pwm_device *pwm, static int stm32_pwm_config(struct stm32_pwm *priv, unsigned int ch, u64 duty_ns, u64 period_ns) { - unsigned long long prd, div, dty; - unsigned int prescaler = 0; + unsigned long long prd, dty; + unsigned long long prescaler; u32 ccmr, mask, shift; /* * .probe() asserted that clk_get_rate() is not bigger than 1 GHz, so - * this won't overflow. + * the calculations here won't overflow. + * First we need to find the minimal value for prescaler such that + * + * period_ns * clkrate + * ------------------------------ + * NSEC_PER_SEC * (prescaler + 1) + * + * isn't bigger than max_arr. */ - div = mul_u64_u64_div_u64(period_ns, clk_get_rate(priv->clk), - NSEC_PER_SEC); - prd = div; - while (div > priv->max_arr) { - prescaler++; - div = prd; - do_div(div, prescaler + 1); - } - - prd = div; + prescaler = mul_u64_u64_div_u64(period_ns, clk_get_rate(priv->clk), + (u64)NSEC_PER_SEC * priv->max_arr); + if (prescaler > 0) + prescaler -= 1; if (prescaler > MAX_TIM_PSC) return -EINVAL; + prd = mul_u64_u64_div_u64(period_ns, clk_get_rate(priv->clk), + (u64)NSEC_PER_SEC * (prescaler + 1)); + /* * All channels share the same prescaler and counter so when two * channels are active at the same time we can't change them