diff options
| author | Fabrice Gasnier <fabrice.gasnier@st.com> | 2018-05-16 09:36:00 +0200 |
|---|---|---|
| committer | Lee Jones <lee.jones@linaro.org> | 2018-05-16 09:11:19 +0100 |
| commit | ab3a897847834bf3e864fb07b733c444895a24ba (patch) | |
| tree | b451c46ce5f7250e455fd71a3598267b8a7f5514 /drivers | |
| parent | d66ffb91c374fc500fe666645184e278774bad38 (diff) | |
pwm: stm32: Use input prescaler to improve period capture
Using input prescaler, capture unit will trigger DMA once every
configurable /2, /4 or /8 events (rising edge). This helps improve
period (only) capture accuracy at high rates.
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/pwm/pwm-stm32.c | 63 |
1 files changed, 61 insertions, 2 deletions
diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c index 9a50acde1e61..60bfc07c4912 100644 --- a/drivers/pwm/pwm-stm32.c +++ b/drivers/pwm/pwm-stm32.c @@ -8,6 +8,7 @@ * pwm-atmel.c from Bo Shen */ +#include <linux/bitfield.h> #include <linux/mfd/stm32-timers.h> #include <linux/module.h> #include <linux/of.h> @@ -168,7 +169,7 @@ static int stm32_pwm_capture(struct pwm_chip *chip, struct pwm_device *pwm, struct stm32_pwm *priv = to_stm32_pwm_dev(chip); unsigned long long prd, div, dty; unsigned long rate; - unsigned int psc = 0, scale; + unsigned int psc = 0, icpsc, scale; u32 raw_prd, raw_dty; int ret = 0; @@ -222,6 +223,7 @@ static int stm32_pwm_capture(struct pwm_chip *chip, struct pwm_device *pwm, /* * Got a capture. Try to improve accuracy at high rates: * - decrease counter clock prescaler, scale up to max rate. + * - use input prescaler, capture once every /2 /4 or /8 edges. */ if (raw_prd) { u32 max_arr = priv->max_arr - 0x1000; /* arbitrary margin */ @@ -241,8 +243,65 @@ static int stm32_pwm_capture(struct pwm_chip *chip, struct pwm_device *pwm, goto stop; } + /* Compute intermediate period not to exceed timeout at low rates */ prd = (unsigned long long)raw_prd * (psc + 1) * NSEC_PER_SEC; - result->period = DIV_ROUND_UP_ULL(prd, rate); + do_div(prd, rate); + + for (icpsc = 0; icpsc < MAX_TIM_ICPSC ; icpsc++) { + /* input prescaler: also keep arbitrary margin */ + if (raw_prd >= (priv->max_arr - 0x1000) >> (icpsc + 1)) + break; + if (prd >= (tmo_ms * NSEC_PER_MSEC) >> (icpsc + 2)) + break; + } + + if (!icpsc) + goto done; + + /* Last chance to improve period accuracy, using input prescaler */ + regmap_update_bits(priv->regmap, + pwm->hwpwm < 2 ? TIM_CCMR1 : TIM_CCMR2, + TIM_CCMR_IC1PSC | TIM_CCMR_IC2PSC, + FIELD_PREP(TIM_CCMR_IC1PSC, icpsc) | + FIELD_PREP(TIM_CCMR_IC2PSC, icpsc)); + + ret = stm32_pwm_raw_capture(priv, pwm, tmo_ms, &raw_prd, &raw_dty); + if (ret) + goto stop; + + if (raw_dty >= (raw_prd >> icpsc)) { + /* + * We may fall here using input prescaler, when input + * capture starts on high side (before falling edge). + * Example with icpsc to capture on each 4 events: + * + * start 1st capture 2nd capture + * v v v + * ___ _____ _____ _____ _____ ____ + * TI1..4 |__| |__| |__| |__| |__| + * v v . . . . . v v + * icpsc1/3: . 0 . 1 . 2 . 3 . 0 + * icpsc2/4: 0 1 2 3 0 + * v v v v + * CCR1/3 ......t0..............................t2 + * CCR2/4 ..t1..............................t1'... + * . . . + * Capture0: .<----------------------------->. + * Capture1: .<-------------------------->. . + * . . . + * Period: .<------> . . + * Low side: .<>. + * + * Result: + * - Period = Capture0 / icpsc + * - Duty = Period - Low side = Period - (Capture0 - Capture1) + */ + raw_dty = (raw_prd >> icpsc) - (raw_prd - raw_dty); + } + +done: + prd = (unsigned long long)raw_prd * (psc + 1) * NSEC_PER_SEC; + result->period = DIV_ROUND_UP_ULL(prd, rate << icpsc); dty = (unsigned long long)raw_dty * (psc + 1) * NSEC_PER_SEC; result->duty_cycle = DIV_ROUND_UP_ULL(dty, rate); stop: |