linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Fabrice Gasnier <fabrice.gasnier@st.com>
To: <lee.jones@linaro.org>, <thierry.reding@gmail.com>,
	<alexandre.torgue@st.com>
Cc: <benjamin.gaignard@linaro.org>, <robh+dt@kernel.org>,
	<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 v3 4/6] pwm: stm32: improve capture by tuning counter prescaler
Date: Fri, 30 Mar 2018 12:01:22 +0200	[thread overview]
Message-ID: <1522404084-24903-5-git-send-email-fabrice.gasnier@st.com> (raw)
In-Reply-To: <1522404084-24903-1-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>
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Acked-by: Thierry Reding <thierry.reding@gmail.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 00c6251..c6eb0a8 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:[~2018-03-30 10:02 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-30 10:01 [PATCH v3 0/6] Add support for PWM input capture on STM32 Fabrice Gasnier
2018-03-30 10:01 ` [PATCH v3 1/6] dt-bindings: mfd: stm32-timers: add support for dmas Fabrice Gasnier
2018-04-16 12:23   ` Lee Jones
2018-04-16 12:23     ` Lee Jones
2018-03-30 10:01 ` [PATCH v3 2/6] " Fabrice Gasnier
2018-04-16 12:22   ` Lee Jones
2018-04-16 12:46     ` Fabrice Gasnier
2018-04-16 14:47       ` Lee Jones
2018-04-16 15:12         ` Fabrice Gasnier
2018-03-30 10:01 ` [PATCH v3 3/6] pwm: stm32: add capture support Fabrice Gasnier
2018-04-16 12:24   ` Lee Jones
2018-03-30 10:01 ` Fabrice Gasnier [this message]
2018-03-30 10:01 ` [PATCH v3 5/6] pwm: stm32: use input prescaler to improve period capture Fabrice Gasnier
2018-04-16 12:25   ` Lee Jones
2018-03-30 10:01 ` [PATCH v3 6/6] ARM: dts: stm32: Enable pwm3 input capture on stm32f429i-eval Fabrice Gasnier

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1522404084-24903-5-git-send-email-fabrice.gasnier@st.com \
    --to=fabrice.gasnier@st.com \
    --cc=alexandre.torgue@st.com \
    --cc=benjamin.gaignard@linaro.org \
    --cc=benjamin.gaignard@st.com \
    --cc=devicetree@vger.kernel.org \
    --cc=lee.jones@linaro.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pwm@vger.kernel.org \
    --cc=linux@armlinux.org.uk \
    --cc=mark.rutland@arm.com \
    --cc=mcoquelin.stm32@gmail.com \
    --cc=robh+dt@kernel.org \
    --cc=thierry.reding@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).