Commit 8002fbee authored by Uwe Kleine-König's avatar Uwe Kleine-König
Browse files

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: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
parent d44d6356

drivers/pwm/pwm-stm32.c

+17 −13
Original line number Diff line number Diff line
@@ -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