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From: Fabrice Gasnier <fabrice.gasnier@st.com>
To: <thierry.reding@gmail.com>
Cc: <u.kleine-koenig@pengutronix.de>, <alexandre.torgue@st.com>,
	<fabrice.gasnier@st.com>, <linux-pwm@vger.kernel.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>,
	<linux-stm32@st-md-mailman.stormreply.com>
Subject: [PATCH v2] pwm: stm32-lp: add check in case requested period cannot be achieved
Date: Wed, 18 Sep 2019 16:54:21 +0200	[thread overview]
Message-ID: <1568818461-19995-1-git-send-email-fabrice.gasnier@st.com> (raw)

LPTimer can use a 32KHz clock for counting. It depends on clock tree
configuration. In such a case, PWM output frequency range is limited.
Although unlikely, nothing prevents user from requesting a PWM frequency
above counting clock (32KHz for instance):
- This causes (prd - 1) = 0xffff to be written in ARR register later in
the apply() routine.
This results in badly configured PWM period (and also duty_cycle).
Add a check to report an error is such a case.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
---
Changes in v2:
- remarks from Uwe: update the comment, use dev_dbg() and print period that
  cannot be reached
---
 drivers/pwm/pwm-stm32-lp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/pwm/pwm-stm32-lp.c b/drivers/pwm/pwm-stm32-lp.c
index 2211a64..97a9afa 100644
--- a/drivers/pwm/pwm-stm32-lp.c
+++ b/drivers/pwm/pwm-stm32-lp.c
@@ -59,6 +59,12 @@ static int stm32_pwm_lp_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	/* Calculate the period and prescaler value */
 	div = (unsigned long long)clk_get_rate(priv->clk) * state->period;
 	do_div(div, NSEC_PER_SEC);
+	if (!div) {
+		/* Clock is too slow to achieve requested period. */
+		dev_dbg(priv->chip.dev, "Can't reach %u ns\n",	state->period);
+		return -EINVAL;
+	}
+
 	prd = div;
 	while (div > STM32_LPTIM_MAX_ARR) {
 		presc++;
-- 
2.7.4


WARNING: multiple messages have this Message-ID (diff)
From: Fabrice Gasnier <fabrice.gasnier@st.com>
To: thierry.reding@gmail.com
Cc: linux-pwm@vger.kernel.org, alexandre.torgue@st.com,
	linux-kernel@vger.kernel.org, u.kleine-koenig@pengutronix.de,
	fabrice.gasnier@st.com, linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] pwm: stm32-lp: add check in case requested period cannot be achieved
Date: Wed, 18 Sep 2019 16:54:21 +0200	[thread overview]
Message-ID: <1568818461-19995-1-git-send-email-fabrice.gasnier@st.com> (raw)

LPTimer can use a 32KHz clock for counting. It depends on clock tree
configuration. In such a case, PWM output frequency range is limited.
Although unlikely, nothing prevents user from requesting a PWM frequency
above counting clock (32KHz for instance):
- This causes (prd - 1) = 0xffff to be written in ARR register later in
the apply() routine.
This results in badly configured PWM period (and also duty_cycle).
Add a check to report an error is such a case.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
---
Changes in v2:
- remarks from Uwe: update the comment, use dev_dbg() and print period that
  cannot be reached
---
 drivers/pwm/pwm-stm32-lp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/pwm/pwm-stm32-lp.c b/drivers/pwm/pwm-stm32-lp.c
index 2211a64..97a9afa 100644
--- a/drivers/pwm/pwm-stm32-lp.c
+++ b/drivers/pwm/pwm-stm32-lp.c
@@ -59,6 +59,12 @@ static int stm32_pwm_lp_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	/* Calculate the period and prescaler value */
 	div = (unsigned long long)clk_get_rate(priv->clk) * state->period;
 	do_div(div, NSEC_PER_SEC);
+	if (!div) {
+		/* Clock is too slow to achieve requested period. */
+		dev_dbg(priv->chip.dev, "Can't reach %u ns\n",	state->period);
+		return -EINVAL;
+	}
+
 	prd = div;
 	while (div > STM32_LPTIM_MAX_ARR) {
 		presc++;
-- 
2.7.4

WARNING: multiple messages have this Message-ID (diff)
From: Fabrice Gasnier <fabrice.gasnier@st.com>
To: <thierry.reding@gmail.com>
Cc: linux-pwm@vger.kernel.org, alexandre.torgue@st.com,
	linux-kernel@vger.kernel.org, u.kleine-koenig@pengutronix.de,
	fabrice.gasnier@st.com, linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] pwm: stm32-lp: add check in case requested period cannot be achieved
Date: Wed, 18 Sep 2019 16:54:21 +0200	[thread overview]
Message-ID: <1568818461-19995-1-git-send-email-fabrice.gasnier@st.com> (raw)

LPTimer can use a 32KHz clock for counting. It depends on clock tree
configuration. In such a case, PWM output frequency range is limited.
Although unlikely, nothing prevents user from requesting a PWM frequency
above counting clock (32KHz for instance):
- This causes (prd - 1) = 0xffff to be written in ARR register later in
the apply() routine.
This results in badly configured PWM period (and also duty_cycle).
Add a check to report an error is such a case.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
---
Changes in v2:
- remarks from Uwe: update the comment, use dev_dbg() and print period that
  cannot be reached
---
 drivers/pwm/pwm-stm32-lp.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/pwm/pwm-stm32-lp.c b/drivers/pwm/pwm-stm32-lp.c
index 2211a64..97a9afa 100644
--- a/drivers/pwm/pwm-stm32-lp.c
+++ b/drivers/pwm/pwm-stm32-lp.c
@@ -59,6 +59,12 @@ static int stm32_pwm_lp_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	/* Calculate the period and prescaler value */
 	div = (unsigned long long)clk_get_rate(priv->clk) * state->period;
 	do_div(div, NSEC_PER_SEC);
+	if (!div) {
+		/* Clock is too slow to achieve requested period. */
+		dev_dbg(priv->chip.dev, "Can't reach %u ns\n",	state->period);
+		return -EINVAL;
+	}
+
 	prd = div;
 	while (div > STM32_LPTIM_MAX_ARR) {
 		presc++;
-- 
2.7.4


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

             reply	other threads:[~2019-09-18 14:55 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-18 14:54 Fabrice Gasnier [this message]
2019-09-18 14:54 ` [PATCH v2] pwm: stm32-lp: add check in case requested period cannot be achieved Fabrice Gasnier
2019-09-18 14:54 ` Fabrice Gasnier
2019-09-18 18:40 ` Uwe Kleine-König
2019-09-18 18:40   ` Uwe Kleine-König

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