[RFC,v4,2/2] pwm: imx: Configure output to GPIO in disabled state
diff mbox series

Message ID 1544616263-82642-3-git-send-email-michal.vokac@ysoft.com
State New
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Series
  • pwm: imx: Configure output to GPIO in disabled state
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Commit Message

Michal Vokáč Dec. 12, 2018, 12:04 p.m. UTC
Normally the PWM output is held LOW when PWM is disabled. This can cause
problems when inverted PWM signal polarity is needed. With this behavior
the connected circuit is fed by 100% duty cycle instead of being shut-off.

Allow users to define a "pwm" and a "gpio" pinctrl states. The pwm pinctrl
state is selected when PWM is enabled and the gpio pinctrl state is
selected when PWM is disabled. In the gpio state the new pwm-gpios GPIO is
configured as input and the internal pull-up resistor is used to pull the
output level high.

If all the pinctrl states and the pwm-gpios GPIO are not correctly
specified in DT the PWM work as usual.

As an example, with this patch a PWM controlled backlight with inversed
signal polarity can be used in full brightness range. Without this patch
the backlight can not be turned off as brightness = 0 disables the PWM
and that in turn set PWM output LOW, that is full brightness.

Inverted output of the PWM with "default" and with "pwm"+"gpio" pinctrl:

+--------------+------------+---------------+----------- +-------------+
| After reset  | Bootloader |   PWM probe   |     PWM    |     PWM     |
| 100k pull-up |            |               | enable 30% |   disable   |
+--------------+------------+---------------+------------+-------------+
| pinctrl      |    none    |    default    |   default  |   default   |
| out H   __________________                   __   __                 |
| out L                     \_________________/  \_/  \_/\____________ |
|                                           ^    ^    ^                |
+--------------+------------+---------------+------------+-------------+
| pinctrl      |    none    |      gpio     |     pwm    |     gpio    |
| out H   __________________________________   __   __   _____________ |
| out L                                     \_/  \_/  \_/              |
|                                           ^    ^    ^                |
+----------------------------------------------------------------------+

Signed-off-by: Michal Vokáč <michal.vokac@ysoft.com>
---
Changes in v4:
 - Get the pinctrl first, if OK only then get the GPIO. (Uwe)
 - Use the non-optional variant of devm_gpiod_get().
 - Align function arguments to the opening parentheses. (Uwe)

Changes in v3:
 - Commit message update.
 - Minor fix in code comment (Uwe)
 - Align function arguments to the opening parentheses. (Uwe)
 - Do not test devm_pinctrl_get for NULL. (Thierry)
 - Convert all messages to dev_dbg() (Thierry)
 - Do not actively drive the pin in gpio state. Configure it as input
   and rely solely on the internal pull-up. (Thierry)

Changes in v2:
 - Utilize the "pwm" and "gpio" pinctrl states.
 - Use the pwm-gpios signal to drive the output in "gpio" pinctrl state.
 - Select the right pinctrl state in probe.


 drivers/pwm/pwm-imx.c | 85 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)

Comments

Uwe Kleine-König Dec. 13, 2018, 8:56 a.m. UTC | #1
Hello,

On Wed, Dec 12, 2018 at 12:04:51PM +0000, Vokáč Michal wrote:
> Normally the PWM output is held LOW when PWM is disabled. This can cause
> problems when inverted PWM signal polarity is needed. With this behavior
> the connected circuit is fed by 100% duty cycle instead of being shut-off.
> 
> Allow users to define a "pwm" and a "gpio" pinctrl states. The pwm pinctrl
> state is selected when PWM is enabled and the gpio pinctrl state is
> selected when PWM is disabled. In the gpio state the new pwm-gpios GPIO is
> configured as input and the internal pull-up resistor is used to pull the
> output level high.
> 
> If all the pinctrl states and the pwm-gpios GPIO are not correctly
> specified in DT the PWM work as usual.
> 
> As an example, with this patch a PWM controlled backlight with inversed
> signal polarity can be used in full brightness range. Without this patch
> the backlight can not be turned off as brightness = 0 disables the PWM
> and that in turn set PWM output LOW, that is full brightness.
> 
> Inverted output of the PWM with "default" and with "pwm"+"gpio" pinctrl:
> 
> +--------------+------------+---------------+----------- +-------------+
> | After reset  | Bootloader |   PWM probe   |     PWM    |     PWM     |
> | 100k pull-up |            |               | enable 30% |   disable   |
> +--------------+------------+---------------+------------+-------------+
> | pinctrl      |    none    |    default    |   default  |   default   |
> | out H   __________________                   __   __                 |
> | out L                     \_________________/  \_/  \_/\____________ |
> |                                           ^    ^    ^                |
> +--------------+------------+---------------+------------+-------------+
> | pinctrl      |    none    |      gpio     |     pwm    |     gpio    |
> | out H   __________________________________   __   __   _____________ |
> | out L                                     \_/  \_/  \_/              |
> |                                           ^    ^    ^                |
> +----------------------------------------------------------------------+

Just for the record: My last concern against this patch set (that I sent
for v3) and v4 of the series criss-crossed. So the problem with the
peaks that could happen is still unaddressed.

Best regards
Uwe
Michal Vokáč Jan. 24, 2019, 8:54 a.m. UTC | #2
On 13.12.2018 09:56, Uwe Kleine-König wrote:
> On Wed, Dec 12, 2018 at 12:04:51PM +0000, Vokáč Michal wrote:
>> Normally the PWM output is held LOW when PWM is disabled. This can cause
>> problems when inverted PWM signal polarity is needed. With this behavior
>> the connected circuit is fed by 100% duty cycle instead of being shut-off.
>>
>> Allow users to define a "pwm" and a "gpio" pinctrl states. The pwm pinctrl
>> state is selected when PWM is enabled and the gpio pinctrl state is
>> selected when PWM is disabled. In the gpio state the new pwm-gpios GPIO is
>> configured as input and the internal pull-up resistor is used to pull the
>> output level high.
>>
>> If all the pinctrl states and the pwm-gpios GPIO are not correctly
>> specified in DT the PWM work as usual.
>>
>> As an example, with this patch a PWM controlled backlight with inversed
>> signal polarity can be used in full brightness range. Without this patch
>> the backlight can not be turned off as brightness = 0 disables the PWM
>> and that in turn set PWM output LOW, that is full brightness.
>>
>> Inverted output of the PWM with "default" and with "pwm"+"gpio" pinctrl:
>>
>> +--------------+------------+---------------+----------- +-------------+
>> | After reset  | Bootloader |   PWM probe   |     PWM    |     PWM     |
>> | 100k pull-up |            |               | enable 30% |   disable   |
>> +--------------+------------+---------------+------------+-------------+
>> | pinctrl      |    none    |    default    |   default  |   default   |
>> | out H   __________________                   __   __                 |
>> | out L                     \_________________/  \_/  \_/\____________ |
>> |                                           ^    ^    ^                |
>> +--------------+------------+---------------+------------+-------------+
>> | pinctrl      |    none    |      gpio     |     pwm    |     gpio    |
>> | out H   __________________________________   __   __   _____________ |
>> | out L                                     \_/  \_/  \_/              |
>> |                                           ^    ^    ^                |
>> +----------------------------------------------------------------------+
> 
> Just for the record: My last concern against this patch set (that I sent
> for v3) and v4 of the series criss-crossed. So the problem with the
> peaks that could happen is still unaddressed.

Hi Uwe et al.

Sorry for the huge delay. I hope we will be able to refresh our
memories and continue on the discussion. I will react to your
comments in the appropriate v3 thread. And sorry for this v4.
I was too fast on the trigger back then..

Michal

Patch
diff mbox series

diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c
index 1d5242c..b8782fe 100644
--- a/drivers/pwm/pwm-imx.c
+++ b/drivers/pwm/pwm-imx.c
@@ -12,10 +12,12 @@ 
 #include <linux/err.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 #include <linux/io.h>
 #include <linux/pwm.h>
 #include <linux/of.h>
 #include <linux/of_device.h>
+#include <linux/pinctrl/consumer.h>
 
 /* i.MX1 and i.MX21 share the same PWM function block: */
 
@@ -52,10 +54,52 @@  struct imx_chip {
 	void __iomem	*mmio_base;
 
 	struct pwm_chip	chip;
+
+	struct pinctrl *pinctrl;
+	struct pinctrl_state *pinctrl_pins_gpio;
+	struct pinctrl_state *pinctrl_pins_pwm;
+	struct gpio_desc *pwm_gpiod;
 };
 
 #define to_imx_chip(chip)	container_of(chip, struct imx_chip, chip)
 
+static int imx_pwm_init_pinctrl_info(struct imx_chip *imx_chip,
+				     struct platform_device *pdev)
+{
+	imx_chip->pinctrl = devm_pinctrl_get(&pdev->dev);
+	if (IS_ERR(imx_chip->pinctrl)) {
+		dev_dbg(&pdev->dev, "can not get pinctrl\n");
+		return PTR_ERR(imx_chip->pinctrl);
+	}
+
+	imx_chip->pinctrl_pins_pwm = pinctrl_lookup_state(imx_chip->pinctrl,
+							  "pwm");
+	imx_chip->pinctrl_pins_gpio = pinctrl_lookup_state(imx_chip->pinctrl,
+							   "gpio");
+
+	if (IS_ERR(imx_chip->pinctrl_pins_pwm) ||
+	    IS_ERR(imx_chip->pinctrl_pins_gpio)) {
+		dev_dbg(&pdev->dev, "pinctrl information incomplete\n");
+		goto out;
+	}
+
+	imx_chip->pwm_gpiod = devm_gpiod_get(&pdev->dev, "pwm", GPIOD_IN);
+	if (PTR_ERR(imx_chip->pwm_gpiod) == -EPROBE_DEFER) {
+		return -EPROBE_DEFER;
+	} else if (IS_ERR(imx_chip->pwm_gpiod)) {
+		dev_dbg(&pdev->dev, "GPIO information incomplete\n");
+		goto out;
+	}
+
+	return 0;
+
+out:
+	devm_pinctrl_put(imx_chip->pinctrl);
+	imx_chip->pinctrl = NULL;
+
+	return 0;
+}
+
 static int imx_pwm_config_v1(struct pwm_chip *chip,
 		struct pwm_device *pwm, int duty_ns, int period_ns)
 {
@@ -216,7 +260,25 @@  static int imx_pwm_apply_v2(struct pwm_chip *chip, struct pwm_device *pwm,
 			cr |= MX3_PWMCR_POUTC;
 
 		writel(cr, imx->mmio_base + MX3_PWMCR);
+
+		/*
+		 * If we are in charge of pinctrl then switch output to
+		 * the PWM signal.
+		 */
+		if (imx->pinctrl)
+			pinctrl_select_state(imx->pinctrl,
+					     imx->pinctrl_pins_pwm);
 	} else if (cstate.enabled) {
+		/*
+		 * PWM block will be disabled. Normally its output will be set
+		 * low no matter what output polarity is configured. Let's use
+		 * pinctrl to switch the output pin to GPIO functon and keep
+		 * the output at the same level as for duty-cycle = 0.
+		 */
+		if (imx->pinctrl)
+			pinctrl_select_state(imx->pinctrl,
+					     imx->pinctrl_pins_gpio);
+
 		writel(0, imx->mmio_base + MX3_PWMCR);
 
 		clk_disable_unprepare(imx->clk_per);
@@ -263,6 +325,7 @@  static int imx_pwm_probe(struct platform_device *pdev)
 	const struct of_device_id *of_id =
 			of_match_device(imx_pwm_dt_ids, &pdev->dev);
 	const struct imx_pwm_data *data;
+	struct pwm_state cstate;
 	struct imx_chip *imx;
 	struct resource *r;
 	int ret = 0;
@@ -294,6 +357,10 @@  static int imx_pwm_probe(struct platform_device *pdev)
 		imx->chip.of_pwm_n_cells = 3;
 	}
 
+	ret = imx_pwm_init_pinctrl_info(imx, pdev);
+	if (ret)
+		return ret;
+
 	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	imx->mmio_base = devm_ioremap_resource(&pdev->dev, r);
 	if (IS_ERR(imx->mmio_base))
@@ -303,6 +370,24 @@  static int imx_pwm_probe(struct platform_device *pdev)
 	if (ret < 0)
 		return ret;
 
+	if (imx->pinctrl) {
+		/*
+		 * Update cstate after pwmchip_add() call as the core might
+		 * call the get_state() function to read the PWM registers
+		 * to get the actual HW state.
+		 */
+		pwm_get_state(imx->chip.pwms, &cstate);
+		if (cstate.enabled) {
+			dev_dbg(&pdev->dev,
+				"PWM entered probe in enabled state\n");
+			pinctrl_select_state(imx->pinctrl,
+					     imx->pinctrl_pins_pwm);
+		} else {
+			pinctrl_select_state(imx->pinctrl,
+					     imx->pinctrl_pins_gpio);
+		}
+	}
+
 	platform_set_drvdata(pdev, imx);
 	return 0;
 }