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gpio: mvebu: pwm fixes and improvements

PATCH In review Baruch Siach 3 participants 7 messages Jan 20, 2021 – Jan 25, 2021

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Baruch Siach

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#0 lore raw

v5 cover gpio: mvebu: pwm fixes and improvements

This series adds a few related fixes to the pwm .apply and .get_state callbacks.

The first patch was originally part of the series adding Armada 8K/7K pwm support. I split it out to a separate series following review comments from Uwe Kleine-König who spotted a few more issues. There is no dependency between this and the Armada 8K/7K series.

v5:

* Drop a patch applied to the gpio tree

* Fix patch 4/4 description typo (Uwe)

* Reduce the number of multiplications (Uwe)

* Add spaces around '+' (Uwe)

* Use '1ULL' instead of explicit cast to reduce verbosity

* Add Linus' Reviewed-by tags to patches that are unchanged since v2

v4:

* Take advantage of zero value being treated as 2^32 by hardware. Rewrite

    patch 5/5 (Uwe).

v3:

* Improve patch 3/5 description (Uwe)

* Add more Reviewed-by tags from Uwe

v2:

Address Uwe Kleine-König comments.

* Improve patch 1/5 summary line

* Add more information to patch 1/5 description

* Add more information to patch 2/5 description

* Don't round period/duty_cycle up in .apply (patch 3/5)

* Expand the comment in path 5/5 based on RMK's analysis of hardware behaviour

* Add Uwe's Reviewed-by tags

Baruch Siach (4):
gpio: mvebu: improve pwm period calculation accuracy
gpio: mvebu: make pwm .get_state closer to idempotent
gpio: mvebu: don't limit pwm period/duty_cycle to UINT_MAX
gpio: mvebu: improve handling of pwm zero on/off values

 drivers/gpio/gpio-mvebu.c | 47 +++++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 22 deletions(-)
Signature · 7 lines
2.29.2


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author
#1 lore raw

PATCH v5 1/4 gpio: mvebu: improve pwm period calculation accuracy

Change 'off' register value calculation from

$off = (period - duty_cycle) * clkrate / NSEC_PER_SEC

to

$off = (period * clkrate / NSEC_PER_SEC) - $on

That is, divide the full period value to reduce rounding error.

Reported-by Uwe Kleine-König <[email protected]>
Reviewed-by Uwe Kleine-König <[email protected]>
Reviewed-by Linus Walleij <[email protected]>
Signed-off-by Baruch Siach <[email protected]>
---
 drivers/gpio/gpio-mvebu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
drivers/gpio/gpio-mvebu.c +2 -2
index a912a8fed197..c424d88e9e2b 100644
@@ -715,9 +715,9 @@ static int mvebu_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	else
 		on = 1;
 
-	val = (unsigned long long) mvpwm->clk_rate *
-		(state->period - state->duty_cycle);
+	val = (unsigned long long) mvpwm->clk_rate * state->period;
 	do_div(val, NSEC_PER_SEC);
+	val -= on;
 	if (val > UINT_MAX)
 		return -EINVAL;
 	if (val)
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2.29.2


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author
#2 lore raw

PATCH v5 2/4 gpio: mvebu: make pwm .get_state closer to idempotent

In reply to Baruch Siach

Round up the divisions in .get_state() to make applying the read out configuration idempotent in most cases as .apply rounds down.

Reported-by Uwe Kleine-König <[email protected]>
Reviewed-by Uwe Kleine-König <[email protected]>
Reviewed-by Linus Walleij <[email protected]>
Signed-off-by Baruch Siach <[email protected]>
---
 drivers/gpio/gpio-mvebu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
drivers/gpio/gpio-mvebu.c +2 -2
index c424d88e9e2b..8673ba77af5a 100644
@@ -668,7 +668,7 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
 
 	regmap_read(mvpwm->regs, mvebu_pwmreg_blink_on_duration(mvpwm), &u);
 	val = (unsigned long long) u * NSEC_PER_SEC;
-	do_div(val, mvpwm->clk_rate);
+	val = DIV_ROUND_UP_ULL(val, mvpwm->clk_rate);
 	if (val > UINT_MAX)
 		state->duty_cycle = UINT_MAX;
 	else if (val)

@@ -680,7 +680,7 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
 	regmap_read(mvpwm->regs, mvebu_pwmreg_blink_off_duration(mvpwm), &u);
 	val += (unsigned long long) u; /* period = on + off duration */
 	val *= NSEC_PER_SEC;
-	do_div(val, mvpwm->clk_rate);
+	val = DIV_ROUND_UP_ULL(val, mvpwm->clk_rate);
 	if (val > UINT_MAX)
 		state->period = UINT_MAX;
 	else if (val)
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2.29.2


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author
#3 lore raw

PATCH v5 3/4 gpio: mvebu: don't limit pwm period/duty_cycle to UINT_MAX

In reply to Baruch Siach

PWM on/off registers are limited to UINT_MAX. However the state period and duty_cycle fields are ns values of type u64. There is no reason to limit them to UINT_MAX.

Reported-by Uwe Kleine-König <[email protected]>
Reviewed-by Uwe Kleine-König <[email protected]>
Reviewed-by Linus Walleij <[email protected]>
Signed-off-by Baruch Siach <[email protected]>
---
 drivers/gpio/gpio-mvebu.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)
drivers/gpio/gpio-mvebu.c +2 -6
index 8673ba77af5a..6b017854ce61 100644
@@ -669,9 +669,7 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
 	regmap_read(mvpwm->regs, mvebu_pwmreg_blink_on_duration(mvpwm), &u);
 	val = (unsigned long long) u * NSEC_PER_SEC;
 	val = DIV_ROUND_UP_ULL(val, mvpwm->clk_rate);
-	if (val > UINT_MAX)
-		state->duty_cycle = UINT_MAX;
-	else if (val)
+	if (val)
 		state->duty_cycle = val;
 	else
 		state->duty_cycle = 1;

@@ -681,9 +679,7 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
 	val += (unsigned long long) u; /* period = on + off duration */
 	val *= NSEC_PER_SEC;
 	val = DIV_ROUND_UP_ULL(val, mvpwm->clk_rate);
-	if (val > UINT_MAX)
-		state->period = UINT_MAX;
-	else if (val)
+	if (val)
 		state->period = val;
 	else
 		state->period = 1;
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2.29.2


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author
#4 lore raw

PATCH v5 4/4 gpio: mvebu: improve handling of pwm zero on/off values

In reply to Baruch Siach

Hardware appears to treat zero value as 2^32. Take advantage of this fact to support on/off values of up to UINT_MAX+1 == 2^32. Adjust both .apply and .get_state to handle zero as a special case.

Rounded up division result in .get_state can't be zero, since the dividend is now larger than 0. Remove check for this case.

Reported-by Uwe Kleine-König <[email protected]>
Analyzed-by Russell King <[email protected]>
Signed-off-by Baruch Siach <[email protected]>
---
 drivers/gpio/gpio-mvebu.c | 39 +++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 16 deletions(-)
drivers/gpio/gpio-mvebu.c +23 -16
index 6b017854ce61..75e3c235bd3a 100644
@@ -667,22 +667,21 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
 	spin_lock_irqsave(&mvpwm->lock, flags);
 
 	regmap_read(mvpwm->regs, mvebu_pwmreg_blink_on_duration(mvpwm), &u);
-	val = (unsigned long long) u * NSEC_PER_SEC;
-	val = DIV_ROUND_UP_ULL(val, mvpwm->clk_rate);
-	if (val)
-		state->duty_cycle = val;
+	/* Hardware treats zero as 2^32. See mvebu_pwm_apply(). */
+	if (u > 0)
+		val = u;
 	else
-		state->duty_cycle = 1;
+		val = UINT_MAX + 1ULL;
+	state->duty_cycle = DIV_ROUND_UP_ULL(val * NSEC_PER_SEC,
+			mvpwm->clk_rate);
 
-	val = (unsigned long long) u; /* on duration */
 	regmap_read(mvpwm->regs, mvebu_pwmreg_blink_off_duration(mvpwm), &u);
-	val += (unsigned long long) u; /* period = on + off duration */
-	val *= NSEC_PER_SEC;
-	val = DIV_ROUND_UP_ULL(val, mvpwm->clk_rate);
-	if (val)
-		state->period = val;
+	/* period = on + off duration */
+	if (u > 0)
+		val += u;
 	else
-		state->period = 1;
+		val += UINT_MAX + 1ULL;
+	state->period = DIV_ROUND_UP_ULL(val * NSEC_PER_SEC, mvpwm->clk_rate);
 
 	regmap_read(mvchip->regs, GPIO_BLINK_EN_OFF + mvchip->offset, &u);
 	if (u)

@@ -704,9 +703,15 @@ static int mvebu_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 
 	val = (unsigned long long) mvpwm->clk_rate * state->duty_cycle;
 	do_div(val, NSEC_PER_SEC);
-	if (val > UINT_MAX)
+	if (val > UINT_MAX + 1ULL)
 		return -EINVAL;
-	if (val)
+	/*
+	 * Zero on/off values don't work as expected. Experimentation shows
+	 * that zero value is treated as 2^32. This behavior is not documented.
+	 */
+	if (val == UINT_MAX + 1ULL)
+		on = 0;
+	else if (val)
 		on = val;
 	else
 		on = 1;

@@ -714,9 +719,11 @@ static int mvebu_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	val = (unsigned long long) mvpwm->clk_rate * state->period;
 	do_div(val, NSEC_PER_SEC);
 	val -= on;
-	if (val > UINT_MAX)
+	if (val > UINT_MAX + 1ULL)
 		return -EINVAL;
-	if (val)
+	if (val == UINT_MAX + 1ULL)
+		off = 0;
+	else if (val)
 		off = val;
 	else
 		off = 1;
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2.29.2


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Reviewed-by on v5 4/4
#5 lore raw

Re: [PATCH v5 4/4] gpio: mvebu: improve handling of pwm zero on/off values

Quoted 10 lines · Baruch Siach

Hardware appears to treat zero value as 2^32. Take advantage of this fact to support on/off values of up to UINT_MAX+1 == 2^32. Adjust both .apply and .get_state to handle zero as a special case.

Rounded up division result in .get_state can't be zero, since the dividend is now larger than 0. Remove check for this case.

Reported-by Uwe Kleine-König <[email protected]>
Analyzed-by Russell King <[email protected]>
Signed-off-by Baruch Siach <[email protected]>
Reviewed-by Uwe Kleine-König <[email protected]>

Thanks
Uwe

Signature · 2 lines
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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#6 lore raw
In reply to Baruch Siach
Quoted 57 lines · Baruch Siach

This series adds a few related fixes to the pwm .apply and .get_state callbacks.

The first patch was originally part of the series adding Armada 8K/7K pwm support. I split it out to a separate series following review comments from Uwe Kleine-König who spotted a few more issues. There is no dependency between this and the Armada 8K/7K series.

v5:

* Drop a patch applied to the gpio tree

* Fix patch 4/4 description typo (Uwe)

* Reduce the number of multiplications (Uwe)

* Add spaces around '+' (Uwe)

* Use '1ULL' instead of explicit cast to reduce verbosity

* Add Linus' Reviewed-by tags to patches that are unchanged since v2

v4:

* Take advantage of zero value being treated as 2^32 by hardware. Rewrite

    patch 5/5 (Uwe).

v3:

* Improve patch 3/5 description (Uwe)

* Add more Reviewed-by tags from Uwe

v2:

Address Uwe Kleine-König comments.

* Improve patch 1/5 summary line

* Add more information to patch 1/5 description

* Add more information to patch 2/5 description

* Don't round period/duty_cycle up in .apply (patch 3/5)

* Expand the comment in path 5/5 based on RMK's analysis of hardware behaviour

* Add Uwe's Reviewed-by tags

Baruch Siach (4):
gpio: mvebu: improve pwm period calculation accuracy
gpio: mvebu: make pwm .get_state closer to idempotent
gpio: mvebu: don't limit pwm period/duty_cycle to UINT_MAX
gpio: mvebu: improve handling of pwm zero on/off values

Quoted 6 lines
 drivers/gpio/gpio-mvebu.c | 47 +++++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 22 deletions(-)

--
2.29.2

Series applied, thanks a lot for the improvements! And thanks to Uwe and Russel for the reviews.

Bartosz

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