From mboxrd@z Thu Jan 1 00:00:00 1970 From: Fabrice Gasnier Subject: [PATCH v2 7/8] pwm: stm32: use input prescaler to improve period capture Date: Fri, 26 Jan 2018 16:11:38 +0100 Message-ID: <1516979499-3665-8-git-send-email-fabrice.gasnier@st.com> References: <1516979499-3665-1-git-send-email-fabrice.gasnier@st.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1516979499-3665-1-git-send-email-fabrice.gasnier@st.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: lee.jones@linaro.org, thierry.reding@gmail.com, robh+dt@kernel.org, alexandre.torgue@st.com, benjamin.gaignard@linaro.org Cc: mark.rutland@arm.com, devicetree@vger.kernel.org, benjamin.gaignard@st.com, linux-pwm@vger.kernel.org, linux@armlinux.org.uk, linux-kernel@vger.kernel.org, mcoquelin.stm32@gmail.com, fabrice.gasnier@st.com, linux-arm-kernel@lists.infradead.org List-Id: devicetree@vger.kernel.org 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 --- Changes in v2: - Adopt DMA read from MFD core. --- drivers/pwm/pwm-stm32.c | 63 ++++++++++++++++++++++++++++++++++++++-- include/linux/mfd/stm32-timers.h | 1 + 2 files changed, 62 insertions(+), 2 deletions(-) diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c index 5dfb296..67964f5 100644 --- a/drivers/pwm/pwm-stm32.c +++ b/drivers/pwm/pwm-stm32.c @@ -9,6 +9,7 @@ * pwm-atmel.c from Bo Shen */ +#include #include #include #include @@ -169,7 +170,7 @@ 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; @@ -223,6 +224,7 @@ 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 */ @@ -242,8 +244,65 @@ 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: diff --git a/include/linux/mfd/stm32-timers.h b/include/linux/mfd/stm32-timers.h index 3abfa04..734cbca 100644 --- a/include/linux/mfd/stm32-timers.h +++ b/include/linux/mfd/stm32-timers.h @@ -82,6 +82,7 @@ #define TIM_DCR_DBL GENMASK(12, 8) /* DMA burst len */ #define MAX_TIM_PSC 0xFFFF +#define MAX_TIM_ICPSC 0x3 #define TIM_CR2_MMS_SHIFT 4 #define TIM_CR2_MMS2_SHIFT 20 #define TIM_SMCR_TS_SHIFT 4 -- 1.9.1