This is a note to let you know that I've just added the patch titled
pwm: stm32: Calculate prescaler with a division instead of a loop
to the 6.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
pwm-stm32-calculate-prescaler-with-a-division-instea.patch
and it can be found in the queue-6.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 44ca2eb625f4693b99d63a97bd906660d3bc16b3
Author: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Date: Sun Mar 17 22:52:16 2024 +0100
pwm: stm32: Calculate prescaler with a division instead of a loop
[ 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>
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
