[PATCH v2] pwm: iqs620a: Correct a stale state variable

[PATCH v2] pwm: iqs620a: Correct a stale state variable

[Jeff LaBundy]

If duty cycle is first set to a value that is sufficiently high to
enable the output (e.g. 10000 ns) but then lowered to a value that
is quantized to zero (e.g. 1000 ns), the output is disabled as the
device cannot drive a constant zero (as expected).

However if the device is later re-initialized due to watchdog bite,
the output is re-enabled at the next-to-last duty cycle (10000 ns).
This is because the iqs620_pwm->out_en flag unconditionally tracks
state->enabled instead of what was actually written to the device.

To solve this problem, use one state variable that encodes all 257
states of the output (duty_scale) with 0 representing tri-state, 1
representing the minimum available duty cycle and 256 representing
100% duty cycle.

Signed-off-by: Jeff LaBundy <jeff@labundy.com>
---
NOTE: This patch is intended to be applied after the following patch:

http://patchwork.ozlabs.org/patch/1426818/

Changes in v2:
  - Collapsed out_en and duty_val into a single state variable (duty_scale)
    that is decoded from the newly added iqs620_pwm_init() function

 drivers/pwm/pwm-iqs620a.c | 88 ++++++++++++++++++++---------------------------
 1 file changed, 37 insertions(+), 51 deletions(-)

diff --git a/drivers/pwm/pwm-iqs620a.c b/drivers/pwm/pwm-iqs620a.c
index 14b18fb..957b972 100644
--- a/drivers/pwm/pwm-iqs620a.c
+++ b/drivers/pwm/pwm-iqs620a.c
@@ -37,15 +37,32 @@ struct iqs620_pwm_private {
 	struct pwm_chip chip;
 	struct notifier_block notifier;
 	struct mutex lock;
-	bool out_en;
-	u8 duty_val;
+	unsigned int duty_scale;
 };

+static int iqs620_pwm_init(struct iqs620_pwm_private *iqs620_pwm,
+			   unsigned int duty_scale)
+{
+	struct iqs62x_core *iqs62x = iqs620_pwm->iqs62x;
+	int ret;
+
+	if (!duty_scale)
+		return regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
+					  IQS620_PWR_SETTINGS_PWM_OUT, 0);
+
+	ret = regmap_write(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE,
+			   duty_scale - 1);
+	if (ret)
+		return ret;
+
+	return regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
+				  IQS620_PWR_SETTINGS_PWM_OUT, 0xff);
+}
+
 static int iqs620_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 			    const struct pwm_state *state)
 {
 	struct iqs620_pwm_private *iqs620_pwm;
-	struct iqs62x_core *iqs62x;
 	unsigned int duty_cycle;
 	unsigned int duty_scale;
 	int ret;
@@ -57,7 +74,6 @@ static int iqs620_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 		return -EINVAL;

 	iqs620_pwm = container_of(chip, struct iqs620_pwm_private, chip);
-	iqs62x = iqs620_pwm->iqs62x;

 	/*
 	 * The duty cycle generated by the device is calculated as follows:
@@ -74,36 +90,15 @@ static int iqs620_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	duty_cycle = min_t(u64, state->duty_cycle, IQS620_PWM_PERIOD_NS);
 	duty_scale = duty_cycle * 256 / IQS620_PWM_PERIOD_NS;

-	mutex_lock(&iqs620_pwm->lock);
-
-	if (!state->enabled || !duty_scale) {
-		ret = regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
-					 IQS620_PWR_SETTINGS_PWM_OUT, 0);
-		if (ret)
-			goto err_mutex;
-	}
-
-	if (duty_scale) {
-		u8 duty_val = duty_scale - 1;
+	if (!state->enabled)
+		duty_scale = 0;

-		ret = regmap_write(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE,
-				   duty_val);
-		if (ret)
-			goto err_mutex;
-
-		iqs620_pwm->duty_val = duty_val;
-	}
-
-	if (state->enabled && duty_scale) {
-		ret = regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
-					 IQS620_PWR_SETTINGS_PWM_OUT, 0xff);
-		if (ret)
-			goto err_mutex;
-	}
+	mutex_lock(&iqs620_pwm->lock);

-	iqs620_pwm->out_en = state->enabled;
+	ret = iqs620_pwm_init(iqs620_pwm, duty_scale);
+	if (!ret)
+		iqs620_pwm->duty_scale = duty_scale;

-err_mutex:
 	mutex_unlock(&iqs620_pwm->lock);

 	return ret;
@@ -121,12 +116,11 @@ static void iqs620_pwm_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
 	/*
 	 * Since the device cannot generate a 0% duty cycle, requests to do so
 	 * cause subsequent calls to iqs620_pwm_get_state to report the output
-	 * as disabled with duty cycle equal to that which was in use prior to
-	 * the request. This is not ideal, but is the best compromise based on
+	 * as disabled. This is not ideal, but is the best compromise based on
 	 * the capabilities of the device.
 	 */
-	state->enabled = iqs620_pwm->out_en;
-	state->duty_cycle = DIV_ROUND_UP((iqs620_pwm->duty_val + 1) *
+	state->enabled = iqs620_pwm->duty_scale > 0;
+	state->duty_cycle = DIV_ROUND_UP(iqs620_pwm->duty_scale *
 					 IQS620_PWM_PERIOD_NS, 256);

 	mutex_unlock(&iqs620_pwm->lock);
@@ -138,7 +132,6 @@ static int iqs620_pwm_notifier(struct notifier_block *notifier,
 			       unsigned long event_flags, void *context)
 {
 	struct iqs620_pwm_private *iqs620_pwm;
-	struct iqs62x_core *iqs62x;
 	int ret;

 	if (!(event_flags & BIT(IQS62X_EVENT_SYS_RESET)))
@@ -146,7 +139,6 @@ static int iqs620_pwm_notifier(struct notifier_block *notifier,

 	iqs620_pwm = container_of(notifier, struct iqs620_pwm_private,
 				  notifier);
-	iqs62x = iqs620_pwm->iqs62x;

 	mutex_lock(&iqs620_pwm->lock);

@@ -155,16 +147,8 @@ static int iqs620_pwm_notifier(struct notifier_block *notifier,
 	 * of a device reset, so nothing else is printed here unless there is
 	 * an additional failure.
 	 */
-	ret = regmap_write(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE,
-			   iqs620_pwm->duty_val);
-	if (ret)
-		goto err_mutex;
+	ret = iqs620_pwm_init(iqs620_pwm, iqs620_pwm->duty_scale);

-	ret = regmap_update_bits(iqs62x->regmap, IQS620_PWR_SETTINGS,
-				 IQS620_PWR_SETTINGS_PWM_OUT,
-				 iqs620_pwm->out_en ? 0xff : 0);
-
-err_mutex:
 	mutex_unlock(&iqs620_pwm->lock);

 	if (ret) {
@@ -211,12 +195,14 @@ static int iqs620_pwm_probe(struct platform_device *pdev)
 	ret = regmap_read(iqs62x->regmap, IQS620_PWR_SETTINGS, &val);
 	if (ret)
 		return ret;
-	iqs620_pwm->out_en = val & IQS620_PWR_SETTINGS_PWM_OUT;

-	ret = regmap_read(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE, &val);
-	if (ret)
-		return ret;
-	iqs620_pwm->duty_val = val;
+	if (val & IQS620_PWR_SETTINGS_PWM_OUT) {
+		ret = regmap_read(iqs62x->regmap, IQS620_PWM_DUTY_CYCLE, &val);
+		if (ret)
+			return ret;
+
+		iqs620_pwm->duty_scale = val + 1;
+	}

 	iqs620_pwm->chip.dev = &pdev->dev;
 	iqs620_pwm->chip.ops = &iqs620_pwm_ops;
--
2.7.4

Re: [PATCH v2] pwm: iqs620a: Correct a stale state variable

[Uwe Kleine-König]

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Hello,

On Mon, Jan 18, 2021 at 10:30:29PM -0600, Jeff LaBundy wrote:
> If duty cycle is first set to a value that is sufficiently high to
> enable the output (e.g. 10000 ns) but then lowered to a value that
> is quantized to zero (e.g. 1000 ns), the output is disabled as the
> device cannot drive a constant zero (as expected).
> 
> However if the device is later re-initialized due to watchdog bite,
> the output is re-enabled at the next-to-last duty cycle (10000 ns).
> This is because the iqs620_pwm->out_en flag unconditionally tracks
> state->enabled instead of what was actually written to the device.
> 
> To solve this problem, use one state variable that encodes all 257
> states of the output (duty_scale) with 0 representing tri-state, 1
> representing the minimum available duty cycle and 256 representing
> 100% duty cycle.
> 
> Signed-off-by: Jeff LaBundy <jeff@labundy.com>

Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

>  1 file changed, 37 insertions(+), 51 deletions(-)

Nice cleanup, thanks for picking up this idea.

Best regards
Uwe

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

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Re: [PATCH v2] pwm: iqs620a: Correct a stale state variable

[Jeff LaBundy]

Hi Thierry,

Do you have any objection to applying Uwe's patch [1] followed by
this one so that they can land in 5.12?

Hi Uwe,

On Fri, Jan 22, 2021 at 07:12:39PM +0100, Uwe Kleine-König wrote:
> Hello,
> 
> On Mon, Jan 18, 2021 at 10:30:29PM -0600, Jeff LaBundy wrote:
> > If duty cycle is first set to a value that is sufficiently high to
> > enable the output (e.g. 10000 ns) but then lowered to a value that
> > is quantized to zero (e.g. 1000 ns), the output is disabled as the
> > device cannot drive a constant zero (as expected).
> > 
> > However if the device is later re-initialized due to watchdog bite,
> > the output is re-enabled at the next-to-last duty cycle (10000 ns).
> > This is because the iqs620_pwm->out_en flag unconditionally tracks
> > state->enabled instead of what was actually written to the device.
> > 
> > To solve this problem, use one state variable that encodes all 257
> > states of the output (duty_scale) with 0 representing tri-state, 1
> > representing the minimum available duty cycle and 256 representing
> > 100% duty cycle.
> > 
> > Signed-off-by: Jeff LaBundy <jeff@labundy.com>
> 
> Reviewed-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> 
> >  1 file changed, 37 insertions(+), 51 deletions(-)
> 
> Nice cleanup, thanks for picking up this idea.

Thank you for your kind words as well as your assistance throughout
this and other patches.

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

Kind regards,
Jeff LaBundy

Re: [PATCH v2] pwm: iqs620a: Correct a stale state variable

[Uwe Kleine-König]

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Hello Jeff,

On Sun, Feb 14, 2021 at 07:19:27PM -0600, Jeff LaBundy wrote:
> Do you have any objection to applying Uwe's patch [1] followed by
> this one so that they can land in 5.12?

FTR: These two patches are in Linus' tree now.
 
Best regards
Uwe

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

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