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From: Fabrice Gasnier <fabrice.gasnier@st.com>
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, linux@armlinux.org.uk,
	mcoquelin.stm32@gmail.com, fabrice.gasnier@st.com,
	benjamin.gaignard@st.com, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org
Subject: [PATCH v2 6/8] pwm: stm32: improve capture by tuning counter prescaler
Date: Fri, 26 Jan 2018 16:11:37 +0100	[thread overview]
Message-ID: <1516979499-3665-7-git-send-email-fabrice.gasnier@st.com> (raw)
In-Reply-To: <1516979499-3665-1-git-send-email-fabrice.gasnier@st.com>

Currently, capture is based on timeout window to configure prescaler.
PWM capture framework provides 1s window at the time of writing.

There's place for improvement, after input signal has been captured once:
- Finer tune counter clock prescaler, by using 1st capture result (with
arbitrary margin).
- Do a 2nd capture, with scaled capture window.
This increases accuracy, especially at high rates.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
---
Changes in v2:
- Adopt DMA read from MFD core.
---
 drivers/pwm/pwm-stm32.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/pwm/pwm-stm32.c b/drivers/pwm/pwm-stm32.c
index f3a92fc..5dfb296 100644
--- a/drivers/pwm/pwm-stm32.c
+++ b/drivers/pwm/pwm-stm32.c
@@ -169,7 +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;
+	unsigned int psc = 0, scale;
 	u32 raw_prd, raw_dty;
 	int ret = 0;
 
@@ -220,6 +220,28 @@ static int stm32_pwm_capture(struct pwm_chip *chip, struct pwm_device *pwm,
 	if (ret)
 		goto stop;
 
+	/*
+	 * Got a capture. Try to improve accuracy at high rates:
+	 * - decrease counter clock prescaler, scale up to max rate.
+	 */
+	if (raw_prd) {
+		u32 max_arr = priv->max_arr - 0x1000; /* arbitrary margin */
+
+		scale = max_arr / min(max_arr, raw_prd);
+	} else {
+		scale = priv->max_arr; /* bellow resolution, use max scale */
+	}
+
+	if (psc && scale > 1) {
+		/* 2nd measure with new scale */
+		psc /= scale;
+		regmap_write(priv->regmap, TIM_PSC, psc);
+		ret = stm32_pwm_raw_capture(priv, pwm, tmo_ms, &raw_prd,
+					    &raw_dty);
+		if (ret)
+			goto stop;
+	}
+
 	prd = (unsigned long long)raw_prd * (psc + 1) * NSEC_PER_SEC;
 	result->period = DIV_ROUND_UP_ULL(prd, rate);
 	dty = (unsigned long long)raw_dty * (psc + 1) * NSEC_PER_SEC;
-- 
1.9.1

  parent reply	other threads:[~2018-01-26 15:11 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-26 15:11 [PATCH v2 0/8] Add support for PWM input capture on STM32 Fabrice Gasnier
2018-01-26 15:11 ` [PATCH v2 1/8] pwm: stm32: fix, remove unused struct device Fabrice Gasnier
2018-01-26 15:11 ` [PATCH v2 2/8] pwm: stm32: protect common prescaler for all channels Fabrice Gasnier
2018-01-26 15:11 ` [PATCH v2 3/8] dt-bindings: mfd: stm32-timers: add support for dmas Fabrice Gasnier
2018-02-05  6:07   ` Rob Herring
2018-01-26 15:11 ` [PATCH v2 4/8] " Fabrice Gasnier
2018-01-26 15:11 ` [PATCH v2 5/8] pwm: stm32: add capture support Fabrice Gasnier
2018-01-26 15:11 ` Fabrice Gasnier [this message]
2018-01-26 15:11 ` [PATCH v2 7/8] pwm: stm32: use input prescaler to improve period capture Fabrice Gasnier
2018-01-26 15:11 ` [PATCH v2 8/8] ARM: dts: stm32: Enable pwm3 input capture on stm32f429i-eval Fabrice Gasnier
2018-01-30 10:15 ` [PATCH v2 0/8] Add support for PWM input capture on STM32 Benjamin Gaignard
2018-02-14  8:23 ` Fabrice Gasnier
     [not found]   ` <5ade7f05-f5cc-e272-842c-22effa78b716-qxv4g6HH51o@public.gmane.org>
2018-02-14  9:38     ` Lee Jones

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