6.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> [ Upstream commit 8002fbeef1e469b2c397d5cd2940e37b32a17849 ] 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@xxxxxxxxxxxxxx Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> Stable-dep-of: c45fcf46ca23 ("pwm: stm32: Refuse too small period requests") Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- 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 27fcc90504f67..1c8911353b81d 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 -- 2.43.0
