[PATCH V3 0/2] pwm: Add GPIO PWM driver

[PATCH V3 0/2] pwm: Add GPIO PWM driver

[Stefan Wahren]

Add a software PWM which toggles a GPIO from a high-resolution timer.

Recent discussions in the Raspberry Pi community revealt that a lot
of users still use MMIO userspace tools for GPIO access. One argument
for this approach is the lack of a GPIO PWM kernel driver. So this
series tries to fill this gap.

This continues the work of Vincent Whitchurch [1], which is easier
to read and more consequent by rejecting sleeping GPIOs than Nicola's
approach [2].

The work has been tested on a Raspberry Pi 3 B+ and a cheap logic
analyzer.

V3:
 - rebase on top of v6.8-pwm-next
 - cherry-pick improvements from Nicola's series
 - try to address Uwe's, Linus' and Andy's comments
 - try to avoid GPIO glitches during probe
 - fix pwm_gpio_remove()
 - some code clean up's and comments

V2:
 - Rename gpio to gpios in binding
 - Calculate next expiry from expected current expiry rather than "now"
 - Only change configuration after current period ends
 - Implement get_state()
 - Add error message for probe failures
 - Stop PWM before unregister

[1] - https://lore.kernel.org/all/20200915135445.al75xmjxudj2rgcp@axis.com/T/
[2] - https://lore.kernel.org/all/20201205214353.xapax46tt5snzd2v@einstein.dilieto.eu/

Nicola Di Lieto (1):
  dt-bindings: pwm: Add pwm-gpio

Vincent Whitchurch (1):
  pwm: Add GPIO PWM driver

 .../devicetree/bindings/pwm/pwm-gpio.yaml     |  42 ++++
 drivers/pwm/Kconfig                           |  11 +
 drivers/pwm/Makefile                          |   1 +
 drivers/pwm/pwm-gpio.c                        | 221 ++++++++++++++++++
 4 files changed, 275 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/pwm/pwm-gpio.yaml
 create mode 100644 drivers/pwm/pwm-gpio.c

--
2.34.1

[PATCH V3 1/2] dt-bindings: pwm: Add pwm-gpio

[Stefan Wahren]

From: Nicola Di Lieto <nicola.dilieto@gmail.com>

Add bindings for the pwm-gpio driver.

Signed-off-by: Nicola Di Lieto <nicola.dilieto@gmail.com>
Co-developed-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
---
 .../devicetree/bindings/pwm/pwm-gpio.yaml     | 42 +++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/pwm/pwm-gpio.yaml

diff --git a/Documentation/devicetree/bindings/pwm/pwm-gpio.yaml b/Documentation/devicetree/bindings/pwm/pwm-gpio.yaml
new file mode 100644
index 000000000000..4932484563f9
--- /dev/null
+++ b/Documentation/devicetree/bindings/pwm/pwm-gpio.yaml
@@ -0,0 +1,42 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/pwm/pwm-gpio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Generic software PWM for modulating GPIOs
+
+maintainers:
+  - Stefan Wahren <wahrenst@gmx.net>
+
+properties:
+  "#pwm-cells":
+    description: |
+      It should be 3. See pwm.yaml in this directory for a
+      description of the cells format.
+    const: 3
+
+  compatible:
+    const: pwm-gpio
+
+  gpios:
+    description:
+      GPIO to be modulated
+    maxItems: 1
+
+required:
+  - "#pwm-cells"
+  - compatible
+  - gpios
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    pwm0 {
+        #pwm-cells = <3>;
+        compatible = "pwm-gpio";
+        gpios = <&gpio 1 GPIO_ACTIVE_HIGH>;
+    };
--
2.34.1

Re: [PATCH V3 1/2] dt-bindings: pwm: Add pwm-gpio

[Conor Dooley]

[-- Attachment #1: Type: text/plain, Size: 2202 bytes --]

On Sun, Jan 28, 2024 at 05:36:29PM +0100, Stefan Wahren wrote:
> From: Nicola Di Lieto <nicola.dilieto@gmail.com>
> 
> Add bindings for the pwm-gpio driver.

drop "driver" from here and instead explain in terms of what the
hardware is doing. I think that's just as simple as saying that it is a
binding for a gpio used as a pwm.

> 
> Signed-off-by: Nicola Di Lieto <nicola.dilieto@gmail.com>
> Co-developed-by: Stefan Wahren <wahrenst@gmx.net>
> Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
> ---
>  .../devicetree/bindings/pwm/pwm-gpio.yaml     | 42 +++++++++++++++++++
>  1 file changed, 42 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/pwm/pwm-gpio.yaml
> 
> diff --git a/Documentation/devicetree/bindings/pwm/pwm-gpio.yaml b/Documentation/devicetree/bindings/pwm/pwm-gpio.yaml
> new file mode 100644
> index 000000000000..4932484563f9
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pwm/pwm-gpio.yaml
> @@ -0,0 +1,42 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/pwm/pwm-gpio.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Generic software PWM for modulating GPIOs
> +
> +maintainers:
> +  - Stefan Wahren <wahrenst@gmx.net>
> +
> +properties:
> +  "#pwm-cells":
> +    description: |
> +      It should be 3. See pwm.yaml in this directory for a
> +      description of the cells format.

Instead of this description (which I know isn't unique to this binding)
I think you should have a ref: to pwm.yaml.

> +    const: 3
> +
> +  compatible:
> +    const: pwm-gpio
> +
> +  gpios:
> +    description:
> +      GPIO to be modulated
> +    maxItems: 1
> +
> +required:
> +  - "#pwm-cells"
> +  - compatible
> +  - gpios
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/gpio/gpio.h>
> +
> +    pwm0 {

Which may then lead to a complaint about the formatting of your node
name.

Cheers,
Conor.

> +        #pwm-cells = <3>;
> +        compatible = "pwm-gpio";
> +        gpios = <&gpio 1 GPIO_ACTIVE_HIGH>;
> +    };
> --
> 2.34.1
> 

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]

[PATCH V3 2/2] pwm: Add GPIO PWM driver

[Stefan Wahren]

From: Vincent Whitchurch <vincent.whitchurch@axis.com>

Add a software PWM which toggles a GPIO from a high-resolution timer.

This will naturally not be as accurate or as efficient as a hardware
PWM, but it is useful in some cases.  I have for example used it for
evaluating LED brightness handling (via leds-pwm) on a board where the
LED was just hooked up to a GPIO, and for a simple verification of the
timer frequency on another platform.

Since high-resolution timers are used, sleeping gpio chips are not
supported and are rejected in the probe function.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Co-developed-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
---
 drivers/pwm/Kconfig    |  11 ++
 drivers/pwm/Makefile   |   1 +
 drivers/pwm/pwm-gpio.c | 221 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 233 insertions(+)
 create mode 100644 drivers/pwm/pwm-gpio.c

diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 4b956d661755..7cfda2cde130 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -227,6 +227,17 @@ config PWM_FSL_FTM
 	  To compile this driver as a module, choose M here: the module
 	  will be called pwm-fsl-ftm.

+config PWM_GPIO
+	tristate "GPIO PWM support"
+	depends on GPIOLIB
+	depends on HIGH_RES_TIMERS
+	help
+	  Generic PWM framework driver for a software PWM toggling a GPIO pin
+	  from kernel high-resolution timers.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called pwm-gpio.
+
 config PWM_HIBVT
 	tristate "HiSilicon BVT PWM support"
 	depends on ARCH_HISI || COMPILE_TEST
diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
index c5ec9e168ee7..59d1a46bb1af 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -19,6 +19,7 @@ obj-$(CONFIG_PWM_DWC_CORE)	+= pwm-dwc-core.o
 obj-$(CONFIG_PWM_DWC)		+= pwm-dwc.o
 obj-$(CONFIG_PWM_EP93XX)	+= pwm-ep93xx.o
 obj-$(CONFIG_PWM_FSL_FTM)	+= pwm-fsl-ftm.o
+obj-$(CONFIG_PWM_GPIO)		+= pwm-gpio.o
 obj-$(CONFIG_PWM_HIBVT)		+= pwm-hibvt.o
 obj-$(CONFIG_PWM_IMG)		+= pwm-img.o
 obj-$(CONFIG_PWM_IMX1)		+= pwm-imx1.o
diff --git a/drivers/pwm/pwm-gpio.c b/drivers/pwm/pwm-gpio.c
new file mode 100644
index 000000000000..14637abe465b
--- /dev/null
+++ b/drivers/pwm/pwm-gpio.c
@@ -0,0 +1,221 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Generic software PWM for modulating GPIOs
+ *
+ * Copyright (C) 2020 Axis Communications AB
+ * Copyright (C) 2020 Nicola Di Lieto
+ * Copyright (C) 2024 Stefan Wahren
+ */
+
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/hrtimer.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+#include <linux/spinlock.h>
+
+struct pwm_gpio {
+	struct pwm_chip chip;
+	struct hrtimer gpio_timer;
+	struct gpio_desc *gpio;
+	struct pwm_state state;
+	struct pwm_state next_state;
+
+	/* Protect internal state between pwm_ops and hrtimer */
+	spinlock_t lock;
+
+	bool changing;
+	bool running;
+	bool level;
+};
+
+static unsigned long pwm_gpio_toggle(struct pwm_gpio *gpwm, bool level)
+{
+	const struct pwm_state *state = &gpwm->state;
+	bool invert = state->polarity == PWM_POLARITY_INVERSED;
+
+	gpwm->level = level;
+	gpiod_set_value(gpwm->gpio, gpwm->level ^ invert);
+
+	if (!state->duty_cycle || state->duty_cycle == state->period) {
+		gpwm->running = false;
+		return 0;
+	}
+
+	gpwm->running = true;
+	return level ? state->duty_cycle : state->period - state->duty_cycle;
+}
+
+static enum hrtimer_restart pwm_gpio_timer(struct hrtimer *gpio_timer)
+{
+	struct pwm_gpio *gpwm = container_of(gpio_timer, struct pwm_gpio,
+					     gpio_timer);
+	unsigned long next_toggle;
+	unsigned long flags;
+	bool new_level;
+
+	spin_lock_irqsave(&gpwm->lock, flags);
+
+	/* Apply new state at end of current period */
+	if (!gpwm->level && gpwm->changing) {
+		gpwm->changing = false;
+		gpwm->state = gpwm->next_state;
+		new_level = !!gpwm->state.duty_cycle;
+	} else {
+		new_level = !gpwm->level;
+	}
+
+	next_toggle = pwm_gpio_toggle(gpwm, new_level);
+	if (next_toggle) {
+		hrtimer_forward(gpio_timer, hrtimer_get_expires(gpio_timer),
+				ns_to_ktime(next_toggle));
+	}
+
+	spin_unlock_irqrestore(&gpwm->lock, flags);
+
+	return next_toggle ? HRTIMER_RESTART : HRTIMER_NORESTART;
+}
+
+static int pwm_gpio_apply(struct pwm_chip *chip, struct pwm_device *pwm,
+			  const struct pwm_state *state)
+{
+	struct pwm_gpio *gpwm = container_of(chip, struct pwm_gpio, chip);
+	bool invert = state->polarity == PWM_POLARITY_INVERSED;
+	unsigned long flags;
+
+	if (!state->enabled) {
+		hrtimer_cancel(&gpwm->gpio_timer);
+	} else if (!gpwm->running) {
+		/*
+		 * This just enables the output, but pwm_gpio_toggle()
+		 * really starts the duty cycle.
+		 */
+		int ret = gpiod_direction_output(gpwm->gpio, invert);
+
+		if (ret)
+			return ret;
+	}
+
+	spin_lock_irqsave(&gpwm->lock, flags);
+
+	if (!state->enabled) {
+		gpwm->state = *state;
+		gpwm->running = false;
+		gpwm->changing = false;
+
+		gpiod_set_value(gpwm->gpio, invert);
+	} else if (gpwm->running) {
+		gpwm->next_state = *state;
+		gpwm->changing = true;
+	} else {
+		unsigned long next_toggle;
+
+		gpwm->state = *state;
+		gpwm->changing = false;
+
+		next_toggle = pwm_gpio_toggle(gpwm, !!state->duty_cycle);
+		if (next_toggle) {
+			hrtimer_start(&gpwm->gpio_timer, next_toggle,
+				      HRTIMER_MODE_REL);
+		}
+	}
+
+	spin_unlock_irqrestore(&gpwm->lock, flags);
+
+	return 0;
+}
+
+static int pwm_gpio_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
+			       struct pwm_state *state)
+{
+	struct pwm_gpio *gpwm = container_of(chip, struct pwm_gpio, chip);
+	unsigned long flags;
+
+	spin_lock_irqsave(&gpwm->lock, flags);
+
+	if (gpwm->changing)
+		*state = gpwm->next_state;
+	else
+		*state = gpwm->state;
+
+	spin_unlock_irqrestore(&gpwm->lock, flags);
+
+	return 0;
+}
+
+static const struct pwm_ops pwm_gpio_ops = {
+	.apply = pwm_gpio_apply,
+	.get_state = pwm_gpio_get_state,
+};
+
+static int pwm_gpio_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct pwm_gpio *gpwm;
+	int ret;
+
+	gpwm = devm_kzalloc(dev, sizeof(*gpwm), GFP_KERNEL);
+	if (!gpwm)
+		return -ENOMEM;
+
+	spin_lock_init(&gpwm->lock);
+
+	gpwm->gpio = devm_gpiod_get(dev, NULL, GPIOD_ASIS);
+	if (IS_ERR(gpwm->gpio)) {
+		return dev_err_probe(dev, PTR_ERR(gpwm->gpio),
+				     "could not get gpio\n");
+	}
+
+	if (gpiod_cansleep(gpwm->gpio)) {
+		return dev_err_probe(dev, -EINVAL,
+				     "sleeping GPIO %d not supported\n",
+				     desc_to_gpio(gpwm->gpio));
+	}
+
+	gpwm->chip.dev = dev;
+	gpwm->chip.ops = &pwm_gpio_ops;
+	gpwm->chip.npwm = 1;
+
+	hrtimer_init(&gpwm->gpio_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	gpwm->gpio_timer.function = pwm_gpio_timer;
+
+	ret = pwmchip_add(&gpwm->chip);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "could not add pwmchip\n");
+
+	platform_set_drvdata(pdev, gpwm);
+
+	return 0;
+}
+
+static void pwm_gpio_remove(struct platform_device *pdev)
+{
+	struct pwm_gpio *gpwm = platform_get_drvdata(pdev);
+
+	pwmchip_remove(&gpwm->chip);
+	hrtimer_cancel(&gpwm->gpio_timer);
+}
+
+static const struct of_device_id pwm_gpio_dt_ids[] = {
+	{ .compatible = "pwm-gpio" },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, pwm_gpio_dt_ids);
+
+static struct platform_driver pwm_gpio_driver = {
+	.driver = {
+		.name = "pwm-gpio",
+		.of_match_table = pwm_gpio_dt_ids,
+	},
+	.probe = pwm_gpio_probe,
+	.remove_new = pwm_gpio_remove,
+};
+module_platform_driver(pwm_gpio_driver);
+
+MODULE_DESCRIPTION("PWM GPIO driver");
+MODULE_ALIAS("platform:pwm-gpio");
+MODULE_AUTHOR("Vincent Whitchurch");
+MODULE_LICENSE("GPL");
--
2.34.1

Re: [PATCH V3 2/2] pwm: Add GPIO PWM driver

[Krzysztof Kozlowski]

On 28/01/2024 17:36, Stefan Wahren wrote:
> From: Vincent Whitchurch <vincent.whitchurch@axis.com>
> 
> Add a software PWM which toggles a GPIO from a high-resolution timer.
> 
> This will naturally not be as accurate or as efficient as a hardware
> PWM, but it is useful in some cases.  I have for example used it for
> evaluating LED brightness handling (via leds-pwm) on a board where the
> LED was just hooked up to a GPIO, and for a simple verification of the
> timer frequency on another platform.
> 

...

> +
> +static struct platform_driver pwm_gpio_driver = {
> +	.driver = {
> +		.name = "pwm-gpio",
> +		.of_match_table = pwm_gpio_dt_ids,
> +	},
> +	.probe = pwm_gpio_probe,
> +	.remove_new = pwm_gpio_remove,
> +};
> +module_platform_driver(pwm_gpio_driver);
> +
> +MODULE_DESCRIPTION("PWM GPIO driver");
> +MODULE_ALIAS("platform:pwm-gpio");

You should not need MODULE_ALIAS() in normal cases. If you need it,
usually it means your device ID table is wrong (e.g. misses either
entries or MODULE_DEVICE_TABLE()). MODULE_ALIAS() is not a substitute
for incomplete ID table.


Best regards,
Krzysztof

Re: [PATCH V3 2/2] pwm: Add GPIO PWM driver

[Linus Walleij]

On Mon, Jan 29, 2024 at 10:40 AM Krzysztof Kozlowski <krzk@kernel.org> wrote:
> On 28/01/2024 17:36, Stefan Wahren wrote:

> > +MODULE_ALIAS("platform:pwm-gpio");
>
> You should not need MODULE_ALIAS() in normal cases. If you need it,
> usually it means your device ID table is wrong (e.g. misses either
> entries or MODULE_DEVICE_TABLE()). MODULE_ALIAS() is not a substitute
> for incomplete ID table.

I was under the impression that MODULE_ALIAS
was something people put in to make platforms using
udev behave better by default, e.g. autoprobing these
devices better (on coldplug for "platform:*").

For example:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4f46d6e7e5ffbce0ee1d1a80767fdf45e56cc863

But I might have got it all wrong :/

Yours,
Linus Walleij

Re: [PATCH V3 2/2] pwm: Add GPIO PWM driver

[Krzysztof Kozlowski]

On 29/01/2024 14:55, Linus Walleij wrote:
> On Mon, Jan 29, 2024 at 10:40 AM Krzysztof Kozlowski <krzk@kernel.org> wrote:
>> On 28/01/2024 17:36, Stefan Wahren wrote:
> 
>>> +MODULE_ALIAS("platform:pwm-gpio");
>>
>> You should not need MODULE_ALIAS() in normal cases. If you need it,
>> usually it means your device ID table is wrong (e.g. misses either
>> entries or MODULE_DEVICE_TABLE()). MODULE_ALIAS() is not a substitute
>> for incomplete ID table.
> 
> I was under the impression that MODULE_ALIAS
> was something people put in to make platforms using
> udev behave better by default, e.g. autoprobing these
> devices better (on coldplug for "platform:*").
> 
> For example:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4f46d6e7e5ffbce0ee1d1a80767fdf45e56cc863
> 
> But I might have got it all wrong :/

That was 2008 :), but answering to the problem: people put MODULE_ALIAS
because they (do not have / forgot / don't want to add)* proper id table
for platform devices with MODULE_DEVICE_TABLE.

While it works, it does not offer the same scalability as proper ID
table and is confusing, because it suggests that driver should be
autoloaded by a platform ID, but not matched/bound by platform ID! Such
situation is very rare and would deserve a comment anyway.

* choose appropriate

See also:
https://lore.kernel.org/all/?q=f%3Akozlowski+drop+unneeded+module_alias


Best regards,
Krzysztof

Re: [PATCH V3 2/2] pwm: Add GPIO PWM driver

[Sean Young]

On Sun, Jan 28, 2024 at 05:36:30PM +0100, Stefan Wahren wrote:
> From: Vincent Whitchurch <vincent.whitchurch@axis.com>
> 
> Add a software PWM which toggles a GPIO from a high-resolution timer.
> 
> This will naturally not be as accurate or as efficient as a hardware
> PWM, but it is useful in some cases.  I have for example used it for
> evaluating LED brightness handling (via leds-pwm) on a board where the
> LED was just hooked up to a GPIO, and for a simple verification of the
> timer frequency on another platform.
> 
> Since high-resolution timers are used, sleeping gpio chips are not
> supported and are rejected in the probe function.
> 
> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
> Co-developed-by: Stefan Wahren <wahrenst@gmx.net>
> Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
> ---
>  drivers/pwm/Kconfig    |  11 ++
>  drivers/pwm/Makefile   |   1 +
>  drivers/pwm/pwm-gpio.c | 221 +++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 233 insertions(+)
>  create mode 100644 drivers/pwm/pwm-gpio.c
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 4b956d661755..7cfda2cde130 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -227,6 +227,17 @@ config PWM_FSL_FTM
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called pwm-fsl-ftm.
> 
> +config PWM_GPIO
> +	tristate "GPIO PWM support"
> +	depends on GPIOLIB
> +	depends on HIGH_RES_TIMERS
> +	help
> +	  Generic PWM framework driver for a software PWM toggling a GPIO pin
> +	  from kernel high-resolution timers.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called pwm-gpio.
> +
>  config PWM_HIBVT
>  	tristate "HiSilicon BVT PWM support"
>  	depends on ARCH_HISI || COMPILE_TEST
> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
> index c5ec9e168ee7..59d1a46bb1af 100644
> --- a/drivers/pwm/Makefile
> +++ b/drivers/pwm/Makefile
> @@ -19,6 +19,7 @@ obj-$(CONFIG_PWM_DWC_CORE)	+= pwm-dwc-core.o
>  obj-$(CONFIG_PWM_DWC)		+= pwm-dwc.o
>  obj-$(CONFIG_PWM_EP93XX)	+= pwm-ep93xx.o
>  obj-$(CONFIG_PWM_FSL_FTM)	+= pwm-fsl-ftm.o
> +obj-$(CONFIG_PWM_GPIO)		+= pwm-gpio.o
>  obj-$(CONFIG_PWM_HIBVT)		+= pwm-hibvt.o
>  obj-$(CONFIG_PWM_IMG)		+= pwm-img.o
>  obj-$(CONFIG_PWM_IMX1)		+= pwm-imx1.o
> diff --git a/drivers/pwm/pwm-gpio.c b/drivers/pwm/pwm-gpio.c
> new file mode 100644
> index 000000000000..14637abe465b
> --- /dev/null
> +++ b/drivers/pwm/pwm-gpio.c
> @@ -0,0 +1,221 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Generic software PWM for modulating GPIOs
> + *
> + * Copyright (C) 2020 Axis Communications AB
> + * Copyright (C) 2020 Nicola Di Lieto
> + * Copyright (C) 2024 Stefan Wahren
> + */
> +
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/hrtimer.h>
> +#include <linux/module.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +#include <linux/spinlock.h>
> +
> +struct pwm_gpio {
> +	struct pwm_chip chip;
> +	struct hrtimer gpio_timer;
> +	struct gpio_desc *gpio;
> +	struct pwm_state state;
> +	struct pwm_state next_state;
> +
> +	/* Protect internal state between pwm_ops and hrtimer */
> +	spinlock_t lock;
> +
> +	bool changing;
> +	bool running;
> +	bool level;
> +};
> +
> +static unsigned long pwm_gpio_toggle(struct pwm_gpio *gpwm, bool level)
> +{
> +	const struct pwm_state *state = &gpwm->state;
> +	bool invert = state->polarity == PWM_POLARITY_INVERSED;
> +
> +	gpwm->level = level;
> +	gpiod_set_value(gpwm->gpio, gpwm->level ^ invert);
> +
> +	if (!state->duty_cycle || state->duty_cycle == state->period) {
> +		gpwm->running = false;
> +		return 0;
> +	}
> +
> +	gpwm->running = true;
> +	return level ? state->duty_cycle : state->period - state->duty_cycle;
> +}
> +
> +static enum hrtimer_restart pwm_gpio_timer(struct hrtimer *gpio_timer)
> +{
> +	struct pwm_gpio *gpwm = container_of(gpio_timer, struct pwm_gpio,
> +					     gpio_timer);
> +	unsigned long next_toggle;
> +	unsigned long flags;
> +	bool new_level;
> +
> +	spin_lock_irqsave(&gpwm->lock, flags);
> +
> +	/* Apply new state at end of current period */
> +	if (!gpwm->level && gpwm->changing) {
> +		gpwm->changing = false;
> +		gpwm->state = gpwm->next_state;
> +		new_level = !!gpwm->state.duty_cycle;
> +	} else {
> +		new_level = !gpwm->level;
> +	}
> +
> +	next_toggle = pwm_gpio_toggle(gpwm, new_level);
> +	if (next_toggle) {
> +		hrtimer_forward(gpio_timer, hrtimer_get_expires(gpio_timer),
> +				ns_to_ktime(next_toggle));
> +	}
> +
> +	spin_unlock_irqrestore(&gpwm->lock, flags);
> +
> +	return next_toggle ? HRTIMER_RESTART : HRTIMER_NORESTART;
> +}
> +
> +static int pwm_gpio_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			  const struct pwm_state *state)
> +{
> +	struct pwm_gpio *gpwm = container_of(chip, struct pwm_gpio, chip);
> +	bool invert = state->polarity == PWM_POLARITY_INVERSED;
> +	unsigned long flags;

Not sure this is necessary but how about:

	if (state->duty_cycle < hrtimer_resolution ||
	    state->period - state->duty_cycle < hrtimer_resolution)
		return -EINVAL;

> +
> +	if (!state->enabled) {
> +		hrtimer_cancel(&gpwm->gpio_timer);
> +	} else if (!gpwm->running) {
> +		/*
> +		 * This just enables the output, but pwm_gpio_toggle()
> +		 * really starts the duty cycle.
> +		 */
> +		int ret = gpiod_direction_output(gpwm->gpio, invert);
> +
> +		if (ret)
> +			return ret;
> +	}
> +
> +	spin_lock_irqsave(&gpwm->lock, flags);
> +
> +	if (!state->enabled) {
> +		gpwm->state = *state;
> +		gpwm->running = false;
> +		gpwm->changing = false;
> +
> +		gpiod_set_value(gpwm->gpio, invert);
> +	} else if (gpwm->running) {
> +		gpwm->next_state = *state;
> +		gpwm->changing = true;
> +	} else {
> +		unsigned long next_toggle;
> +
> +		gpwm->state = *state;
> +		gpwm->changing = false;
> +
> +		next_toggle = pwm_gpio_toggle(gpwm, !!state->duty_cycle);
> +		if (next_toggle) {
> +			hrtimer_start(&gpwm->gpio_timer, next_toggle,
> +				      HRTIMER_MODE_REL);
> +		}
> +	}
> +
> +	spin_unlock_irqrestore(&gpwm->lock, flags);
> +
> +	return 0;
> +}
> +
> +static int pwm_gpio_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
> +			       struct pwm_state *state)
> +{
> +	struct pwm_gpio *gpwm = container_of(chip, struct pwm_gpio, chip);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&gpwm->lock, flags);
> +
> +	if (gpwm->changing)
> +		*state = gpwm->next_state;
> +	else
> +		*state = gpwm->state;
> +
> +	spin_unlock_irqrestore(&gpwm->lock, flags);
> +
> +	return 0;
> +}
> +
> +static const struct pwm_ops pwm_gpio_ops = {
> +	.apply = pwm_gpio_apply,
> +	.get_state = pwm_gpio_get_state,
> +};
> +
> +static int pwm_gpio_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct pwm_gpio *gpwm;
> +	int ret;
> +
> +	gpwm = devm_kzalloc(dev, sizeof(*gpwm), GFP_KERNEL);
> +	if (!gpwm)
> +		return -ENOMEM;
> +
> +	spin_lock_init(&gpwm->lock);
> +
> +	gpwm->gpio = devm_gpiod_get(dev, NULL, GPIOD_ASIS);
> +	if (IS_ERR(gpwm->gpio)) {
> +		return dev_err_probe(dev, PTR_ERR(gpwm->gpio),
> +				     "could not get gpio\n");
> +	}
> +
> +	if (gpiod_cansleep(gpwm->gpio)) {
> +		return dev_err_probe(dev, -EINVAL,
> +				     "sleeping GPIO %d not supported\n",
> +				     desc_to_gpio(gpwm->gpio));
> +	}
> +
> +	gpwm->chip.dev = dev;
> +	gpwm->chip.ops = &pwm_gpio_ops;
> +	gpwm->chip.npwm = 1;

	gpwm->chip.atomic = true; ?

> +
> +	hrtimer_init(&gpwm->gpio_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> +	gpwm->gpio_timer.function = pwm_gpio_timer;
> +
> +	ret = pwmchip_add(&gpwm->chip);
> +	if (ret < 0)
> +		return dev_err_probe(dev, ret, "could not add pwmchip\n");
> +
> +	platform_set_drvdata(pdev, gpwm);
> +
> +	return 0;
> +}
> +
> +static void pwm_gpio_remove(struct platform_device *pdev)
> +{
> +	struct pwm_gpio *gpwm = platform_get_drvdata(pdev);
> +
> +	pwmchip_remove(&gpwm->chip);
> +	hrtimer_cancel(&gpwm->gpio_timer);
> +}
> +
> +static const struct of_device_id pwm_gpio_dt_ids[] = {
> +	{ .compatible = "pwm-gpio" },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, pwm_gpio_dt_ids);
> +
> +static struct platform_driver pwm_gpio_driver = {
> +	.driver = {
> +		.name = "pwm-gpio",
> +		.of_match_table = pwm_gpio_dt_ids,
> +	},
> +	.probe = pwm_gpio_probe,
> +	.remove_new = pwm_gpio_remove,
> +};
> +module_platform_driver(pwm_gpio_driver);
> +
> +MODULE_DESCRIPTION("PWM GPIO driver");
> +MODULE_ALIAS("platform:pwm-gpio");
> +MODULE_AUTHOR("Vincent Whitchurch");
> +MODULE_LICENSE("GPL");
> --
> 2.34.1
> 

Re: [PATCH V3 2/2] pwm: Add GPIO PWM driver

[Stefan Wahren]

Hi Sean,

Am 30.01.24 um 10:08 schrieb Sean Young:
> On Sun, Jan 28, 2024 at 05:36:30PM +0100, Stefan Wahren wrote:
>> From: Vincent Whitchurch <vincent.whitchurch@axis.com>
>>
>> Add a software PWM which toggles a GPIO from a high-resolution timer.
>>
>> This will naturally not be as accurate or as efficient as a hardware
>> PWM, but it is useful in some cases.  I have for example used it for
>> evaluating LED brightness handling (via leds-pwm) on a board where the
>> LED was just hooked up to a GPIO, and for a simple verification of the
>> timer frequency on another platform.
>>
>> Since high-resolution timers are used, sleeping gpio chips are not
>> supported and are rejected in the probe function.
>>
>> Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
>> Co-developed-by: Stefan Wahren <wahrenst@gmx.net>
>> Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
>> ---
...
>> +
>> +static int pwm_gpio_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>> +			  const struct pwm_state *state)
>> +{
>> +	struct pwm_gpio *gpwm = container_of(chip, struct pwm_gpio, chip);
>> +	bool invert = state->polarity == PWM_POLARITY_INVERSED;
>> +	unsigned long flags;
> Not sure this is necessary but how about:
>
> 	if (state->duty_cycle < hrtimer_resolution ||
> 	    state->period - state->duty_cycle < hrtimer_resolution)
> 		return -EINVAL;
>
i think i get the idea, but we need to care about corner cases like
duty_cycle = 0

Re: [PATCH V3 0/2] pwm: Add GPIO PWM driver

[Phil Howard]

On Sun, 28 Jan 2024 at 16:37, Stefan Wahren <wahrenst@gmx.net> wrote:
>
> Add a software PWM which toggles a GPIO from a high-resolution timer.
>
> Recent discussions in the Raspberry Pi community revealt that a lot
> of users still use MMIO userspace tools for GPIO access. One argument
> for this approach is the lack of a GPIO PWM kernel driver. So this
> series tries to fill this gap.

*Thank you* for picking this up. I've been stuck down by covid but am aiming
to build and test this on a Pi 5 (with a gpio chip over PCIe) to see if it runs-
though I am fully expecting a PIO solution (using the Pi 5s RP1) to handle
PWM in this case, and hope to rely upon this gpio-pwm module for previous
iterations.

>
> This continues the work of Vincent Whitchurch [1], which is easier
> to read and more consequent by rejecting sleeping GPIOs than Nicola's
> approach [2].
>
> The work has been tested on a Raspberry Pi 3 B+ and a cheap logic
> analyzer.
>
> V3:
>  - rebase on top of v6.8-pwm-next
>  - cherry-pick improvements from Nicola's series
>  - try to address Uwe's, Linus' and Andy's comments
>  - try to avoid GPIO glitches during probe
>  - fix pwm_gpio_remove()
>  - some code clean up's and comments
>
> V2:
>  - Rename gpio to gpios in binding
>  - Calculate next expiry from expected current expiry rather than "now"
>  - Only change configuration after current period ends
>  - Implement get_state()
>  - Add error message for probe failures
>  - Stop PWM before unregister
>
> [1] - https://lore.kernel.org/all/20200915135445.al75xmjxudj2rgcp@axis.com/T/
> [2] - https://lore.kernel.org/all/20201205214353.xapax46tt5snzd2v@einstein.dilieto.eu/
>
> Nicola Di Lieto (1):
>   dt-bindings: pwm: Add pwm-gpio
>
> Vincent Whitchurch (1):
>   pwm: Add GPIO PWM driver
>
>  .../devicetree/bindings/pwm/pwm-gpio.yaml     |  42 ++++
>  drivers/pwm/Kconfig                           |  11 +
>  drivers/pwm/Makefile                          |   1 +
>  drivers/pwm/pwm-gpio.c                        | 221 ++++++++++++++++++
>  4 files changed, 275 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/pwm/pwm-gpio.yaml
>  create mode 100644 drivers/pwm/pwm-gpio.c
>
> --
> 2.34.1
>

Re: [PATCH V3 0/2] pwm: Add GPIO PWM driver

[Stefan Wahren]

Hi Phil,

Am 02.02.24 um 14:19 schrieb Phil Howard:
> On Sun, 28 Jan 2024 at 16:37, Stefan Wahren <wahrenst@gmx.net> wrote:
>> Add a software PWM which toggles a GPIO from a high-resolution timer.
>>
>> Recent discussions in the Raspberry Pi community revealt that a lot
>> of users still use MMIO userspace tools for GPIO access. One argument
>> for this approach is the lack of a GPIO PWM kernel driver. So this
>> series tries to fill this gap.
> *Thank you* for picking this up. I've been stuck down by covid but am aiming
> to build and test this on a Pi 5 (with a gpio chip over PCIe) to see if it runs-
> though I am fully expecting a PIO solution (using the Pi 5s RP1) to handle
> PWM in this case, and hope to rely upon this gpio-pwm module for previous
> iterations.
i hope you are doing well.

There will be small functional changes in V4. Since this series based on
Linux 6.8 and there is no RPi 5 mainline support, you will need to apply
it on top of rpi-6.8.y.

Should i wait for your test results (no pressure) before sending V4?
>
>> This continues the work of Vincent Whitchurch [1], which is easier
>> to read and more consequent by rejecting sleeping GPIOs than Nicola's
>> approach [2].
>>
>> The work has been tested on a Raspberry Pi 3 B+ and a cheap logic
>> analyzer.
>>
>> V3:
>>   - rebase on top of v6.8-pwm-next
>>   - cherry-pick improvements from Nicola's series
>>   - try to address Uwe's, Linus' and Andy's comments
>>   - try to avoid GPIO glitches during probe
>>   - fix pwm_gpio_remove()
>>   - some code clean up's and comments
>>
>> V2:
>>   - Rename gpio to gpios in binding
>>   - Calculate next expiry from expected current expiry rather than "now"
>>   - Only change configuration after current period ends
>>   - Implement get_state()
>>   - Add error message for probe failures
>>   - Stop PWM before unregister
>>
>> [1] - https://lore.kernel.org/all/20200915135445.al75xmjxudj2rgcp@axis.com/T/
>> [2] - https://lore.kernel.org/all/20201205214353.xapax46tt5snzd2v@einstein.dilieto.eu/
>>
>> Nicola Di Lieto (1):
>>    dt-bindings: pwm: Add pwm-gpio
>>
>> Vincent Whitchurch (1):
>>    pwm: Add GPIO PWM driver
>>
>>   .../devicetree/bindings/pwm/pwm-gpio.yaml     |  42 ++++
>>   drivers/pwm/Kconfig                           |  11 +
>>   drivers/pwm/Makefile                          |   1 +
>>   drivers/pwm/pwm-gpio.c                        | 221 ++++++++++++++++++
>>   4 files changed, 275 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/pwm/pwm-gpio.yaml
>>   create mode 100644 drivers/pwm/pwm-gpio.c
>>
>> --
>> 2.34.1
>>

Re: [PATCH V3 0/2] pwm: Add GPIO PWM driver

[Phil Howard]

On Fri, 2 Feb 2024 at 20:13, Stefan Wahren <wahrenst@gmx.net> wrote:
>
> Hi Phil,
>
> Am 02.02.24 um 14:19 schrieb Phil Howard:
> > On Sun, 28 Jan 2024 at 16:37, Stefan Wahren <wahrenst@gmx.net> wrote:
> >> Add a software PWM which toggles a GPIO from a high-resolution timer.
> >>
> >> Recent discussions in the Raspberry Pi community revealt that a lot
> >> of users still use MMIO userspace tools for GPIO access. One argument
> >> for this approach is the lack of a GPIO PWM kernel driver. So this
> >> series tries to fill this gap.
> > *Thank you* for picking this up. I've been stuck down by covid but am aiming
> > to build and test this on a Pi 5 (with a gpio chip over PCIe) to see if it runs-
> > though I am fully expecting a PIO solution (using the Pi 5s RP1) to handle
> > PWM in this case, and hope to rely upon this gpio-pwm module for previous
> > iterations.
> i hope you are doing well.
>
> There will be small functional changes in V4. Since this series based on
> Linux 6.8 and there is no RPi 5 mainline support, you will need to apply
> it on top of rpi-6.8.y.

I've got as far as applying the patches and building myself a 6.8.y kernel,
just dragging the ol' brain kicking and screaming into dts world again.

>
> Should i wait for your test results (no pressure) before sending V4?

Don't wait on my account- (no really, it's chaos here)- send away!

> >
> >> This continues the work of Vincent Whitchurch [1], which is easier
> >> to read and more consequent by rejecting sleeping GPIOs than Nicola's
> >> approach [2].
> >>
> >> The work has been tested on a Raspberry Pi 3 B+ and a cheap logic
> >> analyzer.
> >>
> >> V3:
> >>   - rebase on top of v6.8-pwm-next
> >>   - cherry-pick improvements from Nicola's series
> >>   - try to address Uwe's, Linus' and Andy's comments
> >>   - try to avoid GPIO glitches during probe
> >>   - fix pwm_gpio_remove()
> >>   - some code clean up's and comments
> >>
> >> V2:
> >>   - Rename gpio to gpios in binding
> >>   - Calculate next expiry from expected current expiry rather than "now"
> >>   - Only change configuration after current period ends
> >>   - Implement get_state()
> >>   - Add error message for probe failures
> >>   - Stop PWM before unregister
> >>
> >> [1] - https://lore.kernel.org/all/20200915135445.al75xmjxudj2rgcp@axis.com/T/
> >> [2] - https://lore.kernel.org/all/20201205214353.xapax46tt5snzd2v@einstein.dilieto.eu/
> >>
> >> Nicola Di Lieto (1):
> >>    dt-bindings: pwm: Add pwm-gpio
> >>
> >> Vincent Whitchurch (1):
> >>    pwm: Add GPIO PWM driver
> >>
> >>   .../devicetree/bindings/pwm/pwm-gpio.yaml     |  42 ++++
> >>   drivers/pwm/Kconfig                           |  11 +
> >>   drivers/pwm/Makefile                          |   1 +
> >>   drivers/pwm/pwm-gpio.c                        | 221 ++++++++++++++++++
> >>   4 files changed, 275 insertions(+)
> >>   create mode 100644 Documentation/devicetree/bindings/pwm/pwm-gpio.yaml
> >>   create mode 100644 drivers/pwm/pwm-gpio.c
> >>
> >> --
> >> 2.34.1
> >>
>


-- 
Philip Howard
Technology & Lifestyle Writer
gadgetoid.com

Gadgetoid gadg-et-oid [gaj-it-oid]

                                     -adjective

1. having the characteristics or form of a gadget; resembling a
mechanical contrivance or device.