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git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
pwm: stm32: Calculate prescaler with a division instead of a loop
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 <u.kleine-koenig@pengutronix.de>
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+17
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drivers/pwm/pwm-stm32.c
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drivers/pwm/pwm-stm32.c
···
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static int stm32_pwm_config(struct stm32_pwm *priv, unsigned int ch,
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u64 duty_ns, u64 period_ns)
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{
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unsigned long long prd, div, dty;
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unsigned int prescaler = 0;
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unsigned long long prd, dty;
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unsigned long long prescaler;
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u32 ccmr, mask, shift;
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/*
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* .probe() asserted that clk_get_rate() is not bigger than 1 GHz, so
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* this won't overflow.
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* the calculations here won't overflow.
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* First we need to find the minimal value for prescaler such that
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*
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* period_ns * clkrate
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* ------------------------------
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* NSEC_PER_SEC * (prescaler + 1)
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*
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* isn't bigger than max_arr.
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*/
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div = mul_u64_u64_div_u64(period_ns, clk_get_rate(priv->clk),
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NSEC_PER_SEC);
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prd = div;
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while (div > priv->max_arr) {
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prescaler++;
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div = prd;
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do_div(div, prescaler + 1);
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}
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prd = div;
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prescaler = mul_u64_u64_div_u64(period_ns, clk_get_rate(priv->clk),
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(u64)NSEC_PER_SEC * priv->max_arr);
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if (prescaler > 0)
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prescaler -= 1;
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if (prescaler > MAX_TIM_PSC)
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return -EINVAL;
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prd = mul_u64_u64_div_u64(period_ns, clk_get_rate(priv->clk),
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(u64)NSEC_PER_SEC * (prescaler + 1));
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/*
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* All channels share the same prescaler and counter so when two