[PATCH v2 0/5] 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.

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 (5):
  gpio: mvebu: fix pwm .get_state period calculation
  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: document zero pwm duty cycle limitation

 drivers/gpio/gpio-mvebu.c | 33 +++++++++++++++------------------
 1 file changed, 15 insertions(+), 18 deletions(-)

-- 
2.29.2


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The period is the sum of on and off values. That is, calculate period as

  ($on + $off) / clkrate

instead of

  $off / clkrate - $on / clkrate

that makes no sense.

Reported-by: Russell King <linux@armlinux.org.uk>
Fixes: 757642f9a584e ("gpio: mvebu: Add limited PWM support")
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
 drivers/gpio/gpio-mvebu.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
index 672681a976f5..a912a8fed197 100644
--- a/drivers/gpio/gpio-mvebu.c
+++ b/drivers/gpio/gpio-mvebu.c

@@ -676,20 +676,17 @@ static void mvebu_pwm_get_state(struct pwm_chip *chip,
 	else
 		state->duty_cycle = 1;
 
+	val = (unsigned long long) u; /* on duration */
 	regmap_read(mvpwm->regs, mvebu_pwmreg_blink_off_duration(mvpwm), &u);
-	val = (unsigned long long) u * NSEC_PER_SEC;
+	val += (unsigned long long) u; /* period = on + off duration */
+	val *= NSEC_PER_SEC;
 	do_div(val, mvpwm->clk_rate);
-	if (val < state->duty_cycle) {
+	if (val > UINT_MAX)
+		state->period = UINT_MAX;
+	else if (val)
+		state->period = val;
+	else
 		state->period = 1;
-	} else {
-		val -= state->duty_cycle;
-		if (val > UINT_MAX)
-			state->period = UINT_MAX;
-		else if (val)
-			state->period = val;
-		else
-			state->period = 1;
-	}
 
 	regmap_read(mvchip->regs, GPIO_BLINK_EN_OFF + mvchip->offset, &u);
 	if (u)

-- 
2.29.2


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On Wed, Jan 13, 2021 at 11:22:41AM +0200, Baruch Siach wrote:

The period is the sum of on and off values. That is, calculate period as

  ($on + $off) / clkrate

instead of

  $off / clkrate - $on / clkrate

that makes no sense.

Reported-by: Russell King <linux@armlinux.org.uk>
Fixes: 757642f9a584e ("gpio: mvebu: Add limited PWM support")
Signed-off-by: Baruch Siach <baruch@tkos.co.il>

Reviewed-by: Uwe Kleine-König <redacted>

Best regards
Uwe

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

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 <redacted>
Reviewed-by: Uwe Kleine-König <redacted>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
 drivers/gpio/gpio-mvebu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
index a912a8fed197..c424d88e9e2b 100644
--- a/drivers/gpio/gpio-mvebu.c
+++ b/drivers/gpio/gpio-mvebu.c

@@ -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)

-- 
2.29.2


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Round up the result of division in period/duty_cycle calculation to make
the result closer to idempotent.

Reported-by: Uwe Kleine-König <redacted>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
 drivers/gpio/gpio-mvebu.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
index c424d88e9e2b..8673ba77af5a 100644
--- a/drivers/gpio/gpio-mvebu.c
+++ b/drivers/gpio/gpio-mvebu.c

@@ -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)

-- 
2.29.2


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On Wed, Jan 13, 2021 at 11:22:43AM +0200, Baruch Siach wrote:

Round up the result of division in period/duty_cycle calculation to make
the result closer to idempotent.

Maybe:

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 <redacted>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>

Other than that:

Reviewed-by: Uwe Kleine-König <redacted>

Best regards
Uwe

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

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 <redacted>
Reviewed-by: Uwe Kleine-König <redacted>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
 drivers/gpio/gpio-mvebu.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
index 8673ba77af5a..6b017854ce61 100644
--- a/drivers/gpio/gpio-mvebu.c
+++ b/drivers/gpio/gpio-mvebu.c

@@ -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;

-- 
2.29.2


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Add a comment on why the code never sets on/off registers to zero.

Reported-by: Uwe Kleine-König <redacted>
Analyzed-by: Russell King [off-list ref]
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
 drivers/gpio/gpio-mvebu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpio/gpio-mvebu.c b/drivers/gpio/gpio-mvebu.c
index 6b017854ce61..09780944bef9 100644
--- a/drivers/gpio/gpio-mvebu.c
+++ b/drivers/gpio/gpio-mvebu.c

@@ -706,6 +706,10 @@ static int mvebu_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	do_div(val, NSEC_PER_SEC);
 	if (val > UINT_MAX)
 		return -EINVAL;
+	/*
+	 * 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)
 		on = val;
 	else

-- 
2.29.2


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On Wed, Jan 13, 2021 at 10:23 AM Baruch Siach [off-list ref] wrote:

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.

This version looks really good and +/- minor tweaks as indicated by
Uwe:
Reviewed-by: Linus Walleij <redacted>

Yours,
Linus Walleij

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Hello Linus,

On Mon, Jan 18, 2021 at 02:45:14PM +0100, Linus Walleij wrote:

On Wed, Jan 13, 2021 at 10:23 AM Baruch Siach [off-list ref] wrote:

quoted

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.

This version looks really good and +/- minor tweaks as indicated by
Uwe:
Reviewed-by: Linus Walleij <redacted>

The most recent version of this series is v4.

Best regards
Uwe

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