* [PATCH v7 1/2] dt-bindings: pwm: Add pwm-gpio
2024-06-04 21:00 [PATCH v7 0/2] pwm: Add GPIO PWM driver Linus Walleij
@ 2024-06-04 21:00 ` Linus Walleij
2024-06-04 21:00 ` [PATCH v7 2/2] pwm: Add GPIO PWM driver Linus Walleij
` (2 subsequent siblings)
3 siblings, 0 replies; 7+ messages in thread
From: Linus Walleij @ 2024-06-04 21:00 UTC (permalink / raw)
To: Uwe Kleine-König, Rob Herring, Krzysztof Kozlowski,
Conor Dooley, andy.shevchenko, Philip Howard, Sean Young,
Chris Morgan, Stefan Wahren, linux-gpio, linux-pwm, devicetree
Cc: Linus Walleij, Nicola Di Lieto, Krzysztof Kozlowski, Dhruva Gole
From: Nicola Di Lieto <nicola.dilieto@gmail.com>
Add bindings for PWM modulated by GPIO.
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>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
.../devicetree/bindings/pwm/pwm-gpio.yaml | 46 ++++++++++++++++++++++
1 file changed, 46 insertions(+)
diff --git a/Documentation/devicetree/bindings/pwm/pwm-gpio.yaml b/Documentation/devicetree/bindings/pwm/pwm-gpio.yaml
new file mode 100644
index 000000000000..1576c193f2ab
--- /dev/null
+++ b/Documentation/devicetree/bindings/pwm/pwm-gpio.yaml
@@ -0,0 +1,46 @@
+# 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>
+
+allOf:
+ - $ref: pwm.yaml#
+
+properties:
+ compatible:
+ const: pwm-gpio
+
+ "#pwm-cells":
+ const: 3
+ description:
+ See pwm.yaml in this directory for a description of the cells format.
+ The first cell which represents the PWM instance number must always
+ be zero.
+
+ gpios:
+ description:
+ GPIO to be modulated
+ maxItems: 1
+
+required:
+ - compatible
+ - "#pwm-cells"
+ - gpios
+
+additionalProperties: false
+
+examples:
+ - |
+ #include <dt-bindings/gpio/gpio.h>
+
+ pwm {
+ #pwm-cells = <3>;
+ compatible = "pwm-gpio";
+ gpios = <&gpio 1 GPIO_ACTIVE_HIGH>;
+ };
--
2.45.1
^ permalink raw reply related [flat|nested] 7+ messages in thread* [PATCH v7 2/2] pwm: Add GPIO PWM driver
2024-06-04 21:00 [PATCH v7 0/2] pwm: Add GPIO PWM driver Linus Walleij
2024-06-04 21:00 ` [PATCH v7 1/2] dt-bindings: pwm: Add pwm-gpio Linus Walleij
@ 2024-06-04 21:00 ` Linus Walleij
2024-06-05 5:52 ` Dhruva Gole
2024-06-18 11:51 ` [PATCH v7 0/2] " Phil Howard
2024-06-27 6:52 ` Uwe Kleine-König
3 siblings, 1 reply; 7+ messages in thread
From: Linus Walleij @ 2024-06-04 21:00 UTC (permalink / raw)
To: Uwe Kleine-König, Rob Herring, Krzysztof Kozlowski,
Conor Dooley, andy.shevchenko, Philip Howard, Sean Young,
Chris Morgan, Stefan Wahren, linux-gpio, linux-pwm, devicetree
Cc: Linus Walleij, Vincent Whitchurch, Andy Shevchenko
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>
Co-developed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
Documentation/driver-api/gpio/drivers-on-gpio.rst | 7 +-
drivers/pwm/Kconfig | 11 +
drivers/pwm/Makefile | 1 +
drivers/pwm/pwm-gpio.c | 241 ++++++++++++++++++++++
4 files changed, 259 insertions(+), 1 deletion(-)
diff --git a/Documentation/driver-api/gpio/drivers-on-gpio.rst b/Documentation/driver-api/gpio/drivers-on-gpio.rst
index af632d764ac6..95572d2a94ce 100644
--- a/Documentation/driver-api/gpio/drivers-on-gpio.rst
+++ b/Documentation/driver-api/gpio/drivers-on-gpio.rst
@@ -27,7 +27,12 @@ hardware descriptions such as device tree or ACPI:
to the lines for a more permanent solution of this type.
- gpio-beeper: drivers/input/misc/gpio-beeper.c is used to provide a beep from
- an external speaker connected to a GPIO line.
+ an external speaker connected to a GPIO line. (If the beep is controlled by
+ off/on, for an actual PWM waveform, see pwm-gpio below.)
+
+- pwm-gpio: drivers/pwm/pwm-gpio.c is used to toggle a GPIO with a high
+ resolution timer producing a PWM waveform on the GPIO line, as well as
+ Linux high resolution timers can do.
- extcon-gpio: drivers/extcon/extcon-gpio.c is used when you need to read an
external connector status, such as a headset line for an audio driver or an
diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
index 1dd7921194f5..68ba28d52c4c 100644
--- a/drivers/pwm/Kconfig
+++ b/drivers/pwm/Kconfig
@@ -223,6 +223,17 @@ 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 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 90913519f11a..65d62cc41a8f 100644
--- a/drivers/pwm/Makefile
+++ b/drivers/pwm/Makefile
@@ -18,6 +18,7 @@ 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..9f8884ac7504
--- /dev/null
+++ b/drivers/pwm/pwm-gpio.c
@@ -0,0 +1,241 @@
+// 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
+ * Copyright (C) 2024 Linus Walleij
+ */
+
+#include <linux/cleanup.h>
+#include <linux/container_of.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/hrtimer.h>
+#include <linux/math.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/pwm.h>
+#include <linux/spinlock.h>
+#include <linux/time.h>
+#include <linux/types.h>
+
+struct pwm_gpio {
+ 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 void pwm_gpio_round(struct pwm_state *dest, const struct pwm_state *src)
+{
+ u64 dividend;
+ u32 remainder;
+
+ *dest = *src;
+
+ /* Round down to hrtimer resolution */
+ dividend = dest->period;
+ remainder = do_div(dividend, hrtimer_resolution);
+ dest->period -= remainder;
+
+ dividend = dest->duty_cycle;
+ remainder = do_div(dividend, hrtimer_resolution);
+ dest->duty_cycle -= remainder;
+}
+
+static u64 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);
+ u64 next_toggle;
+ bool new_level;
+
+ guard(spinlock_irqsave)(&gpwm->lock);
+
+ /* 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));
+
+ 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 = pwmchip_get_drvdata(chip);
+ bool invert = state->polarity == PWM_POLARITY_INVERSED;
+
+ if (state->duty_cycle && state->duty_cycle < hrtimer_resolution)
+ return -EINVAL;
+
+ if (state->duty_cycle != state->period &&
+ (state->period - state->duty_cycle < hrtimer_resolution))
+ return -EINVAL;
+
+ if (!state->enabled) {
+ hrtimer_cancel(&gpwm->gpio_timer);
+ } else if (!gpwm->running) {
+ int ret;
+
+ /*
+ * This just enables the output, but pwm_gpio_toggle()
+ * really starts the duty cycle.
+ */
+ ret = gpiod_direction_output(gpwm->gpio, invert);
+ if (ret)
+ return ret;
+ }
+
+ guard(spinlock_irqsave)(&gpwm->lock);
+
+ if (!state->enabled) {
+ pwm_gpio_round(&gpwm->state, state);
+ gpwm->running = false;
+ gpwm->changing = false;
+
+ gpiod_set_value(gpwm->gpio, invert);
+ } else if (gpwm->running) {
+ pwm_gpio_round(&gpwm->next_state, state);
+ gpwm->changing = true;
+ } else {
+ unsigned long next_toggle;
+
+ pwm_gpio_round(&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);
+ }
+
+ return 0;
+}
+
+static int pwm_gpio_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
+ struct pwm_state *state)
+{
+ struct pwm_gpio *gpwm = pwmchip_get_drvdata(chip);
+
+ guard(spinlock_irqsave)(&gpwm->lock);
+
+ if (gpwm->changing)
+ *state = gpwm->next_state;
+ else
+ *state = gpwm->state;
+
+ return 0;
+}
+
+static const struct pwm_ops pwm_gpio_ops = {
+ .apply = pwm_gpio_apply,
+ .get_state = pwm_gpio_get_state,
+};
+
+static void pwm_gpio_disable_hrtimer(void *data)
+{
+ struct pwm_gpio *gpwm = data;
+
+ hrtimer_cancel(&gpwm->gpio_timer);
+}
+
+static int pwm_gpio_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct pwm_chip *chip;
+ struct pwm_gpio *gpwm;
+ int ret;
+
+ chip = devm_pwmchip_alloc(dev, 1, sizeof(*gpwm));
+ if (IS_ERR(chip))
+ return PTR_ERR(chip);
+
+ gpwm = pwmchip_get_drvdata(chip);
+
+ 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),
+ "%pfw: could not get gpio\n",
+ dev_fwnode(dev));
+
+ if (gpiod_cansleep(gpwm->gpio))
+ return dev_err_probe(dev, -EINVAL,
+ "%pfw: sleeping GPIO not supported\n",
+ dev_fwnode(dev));
+
+ chip->ops = &pwm_gpio_ops;
+ chip->atomic = true;
+
+ hrtimer_init(&gpwm->gpio_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ ret = devm_add_action_or_reset(dev, pwm_gpio_disable_hrtimer, gpwm);
+ if (ret)
+ return ret;
+
+ gpwm->gpio_timer.function = pwm_gpio_timer;
+
+ ret = pwmchip_add(chip);
+ if (ret < 0)
+ return dev_err_probe(dev, ret, "could not add pwmchip\n");
+
+ return 0;
+}
+
+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,
+};
+module_platform_driver(pwm_gpio_driver);
+
+MODULE_DESCRIPTION("PWM GPIO driver");
+MODULE_AUTHOR("Vincent Whitchurch");
+MODULE_LICENSE("GPL");
--
2.45.1
^ permalink raw reply related [flat|nested] 7+ messages in thread* Re: [PATCH v7 0/2] pwm: Add GPIO PWM driver
2024-06-04 21:00 [PATCH v7 0/2] pwm: Add GPIO PWM driver Linus Walleij
2024-06-04 21:00 ` [PATCH v7 1/2] dt-bindings: pwm: Add pwm-gpio Linus Walleij
2024-06-04 21:00 ` [PATCH v7 2/2] pwm: Add GPIO PWM driver Linus Walleij
@ 2024-06-18 11:51 ` Phil Howard
2024-06-27 6:52 ` Uwe Kleine-König
3 siblings, 0 replies; 7+ messages in thread
From: Phil Howard @ 2024-06-18 11:51 UTC (permalink / raw)
To: Linus Walleij
Cc: Uwe Kleine-König, Rob Herring, Krzysztof Kozlowski,
Conor Dooley, andy.shevchenko, Sean Young, Chris Morgan,
Stefan Wahren, linux-gpio, linux-pwm, devicetree, Nicola Di Lieto,
Krzysztof Kozlowski, Dhruva Gole, Vincent Whitchurch,
Andy Shevchenko
On Tue, 4 Jun 2024 at 22:00, Linus Walleij <linus.walleij@linaro.org> 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.
>
> 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]. It further takes over where Stefan Wahren left off.
>
> I have not looked into the interrupt storm problem mentioned in [3]
> but instead focused on some real-life tests:
>
> The IXP4xx NSLU2 has a speaker connected directly to a GPIO, and I
> wanted to use this patch to provide a proper beeper for the machine
> and not have to rely on custom hacks.
>
> I added a DTS patch like this:
>
> gpio_pwm: pwm {
> #pwm-cells = <3>;
> compatible = "pwm-gpio";
> gpios = <&gpio0 4 GPIO_ACTIVE_HIGH>;
> };
>
> beeper {
> compatible = "pwm-beeper";
> pwms = <&gpio_pwm 0 1 0>;
> beeper-hz = <1000>;
> };
>
> Then activated the necessary drivers with input evdev and they
> both probe fine. Then I use this test program:
> https://gist.github.com/licheegh/3dbdc8918325e8af8d4d13805cd0c350
> with a few different beep frequencies, such as "beep 400"
> for an OK sounding 400 Hz signal.
>
> Above ~10000 Hz the sound becomes bad and mostly sound like
> different kinds of noise. But this is not so bad for the NSLU2
> which is a 266 MHz ARM XScale machine, and we do not need any better
> on this machine so mission accomplished. Pushing the playback
> to higher and higher rates does not crash the machine, the
> sample program always terminates.
>
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
> Changes in v7:
> - Drop platform_set_drvdata() as nothing use this anymore.
> - Add a small blurb documenting the pwm-cells in the binding.
> - Link to v6: https://lore.kernel.org/r/20240602-pwm-gpio-v6-0-e8f6ec9cc783@linaro.org
>
> v6:
> - Add a small blurb to drivers-on-gpio.rst
> - Add missing headers to driver
> - Use guarded spinlocks from <linux/cleanup.h>
> - Drop minor surplus whitespace
> - Use dev pointer everywhere in probe()
> - Drop dev_info() chatter at end of probe()
> - Use devm_add_action_or_reset() for a hook to disable the hrtimer and
> get rid of the .remove() callback altogether.
>
> V5:
> - add Reviewed-by's for dt-binding patch
> - rebase on top of v6.10-rc1
> - print hr resolution at driver probe
> - fix grammar in Kconfig
> - fix return type of pwm_gpio_toggle
> - implement hrtimer resolution rounding as noted by Uwe
> - use firmware node path instead of GPIO numbers as suggested by Andy
> - adjust some header includes and style issues as noted by Andy
>
> V4:
> - address DT bindings comments from Conor Dooley
> - drop unnecessary MODULE_ALIAS() as suggested by Krzysztof Kozlowski
> - add range checks to apply which consider the hrtimer resolution
> (idea comes from Sean Young)
> - mark driver as atomic as suggested by Sean Young
>
> 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/
> [3] - https://lore.kernel.org/linux-pwm/CACRpkdary+kDrTJ=u4VbSTv7wXGLQj9_fy7mv0w-Zg+eDvGXVQ@mail.gmail.com/T/#m513f255daa9f30c325d11999cacd086411591bf9
>
> ---
> Nicola Di Lieto (1):
> dt-bindings: pwm: Add pwm-gpio
>
> Vincent Whitchurch (1):
> pwm: Add GPIO PWM driver
>
> .../devicetree/bindings/pwm/pwm-gpio.yaml | 46 ++++
> Documentation/driver-api/gpio/drivers-on-gpio.rst | 7 +-
> drivers/pwm/Kconfig | 11 +
> drivers/pwm/Makefile | 1 +
> drivers/pwm/pwm-gpio.c | 241 +++++++++++++++++++++
> 5 files changed, 305 insertions(+), 1 deletion(-)
> ---
> base-commit: cc97b8f37b097a1598410154ca472964a1d9b255
> change-id: 20240530-pwm-gpio-e9133a1806ec
>
> Best regards,
> --
> Linus Walleij <linus.walleij@linaro.org>
>
Thank you for picking this up, it's reassuring to see it making progress.
I will give it a shot today.
- Phil
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH v7 0/2] pwm: Add GPIO PWM driver
2024-06-04 21:00 [PATCH v7 0/2] pwm: Add GPIO PWM driver Linus Walleij
` (2 preceding siblings ...)
2024-06-18 11:51 ` [PATCH v7 0/2] " Phil Howard
@ 2024-06-27 6:52 ` Uwe Kleine-König
2024-06-27 9:54 ` Stefan Wahren
3 siblings, 1 reply; 7+ messages in thread
From: Uwe Kleine-König @ 2024-06-27 6:52 UTC (permalink / raw)
To: Linus Walleij
Cc: Rob Herring, Krzysztof Kozlowski, Conor Dooley, andy.shevchenko,
Philip Howard, Sean Young, Chris Morgan, Stefan Wahren,
linux-gpio, linux-pwm, devicetree, Nicola Di Lieto,
Krzysztof Kozlowski, Dhruva Gole, Vincent Whitchurch,
Andy Shevchenko
[-- Attachment #1: Type: text/plain, Size: 1356 bytes --]
Hello,
On Tue, Jun 04, 2024 at 11:00:39PM +0200, Linus Walleij 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.
>
> 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]. It further takes over where Stefan Wahren left off.
>
> I have not looked into the interrupt storm problem mentioned in [3]
> but instead focused on some real-life tests:
>
> The IXP4xx NSLU2 has a speaker connected directly to a GPIO, and I
> wanted to use this patch to provide a proper beeper for the machine
> and not have to rely on custom hacks.
>
> I added a DTS patch like this:
>
> gpio_pwm: pwm {
> #pwm-cells = <3>;
> compatible = "pwm-gpio";
> gpios = <&gpio0 4 GPIO_ACTIVE_HIGH>;
> };
>
> beeper {
> compatible = "pwm-beeper";
> pwms = <&gpio_pwm 0 1 0>;
> beeper-hz = <1000>;
> };
Applied both patches to
https://git.kernel.org/pub/scm/linux/kernel/git/ukleinek/linux.git pwm/for-next
Thanks
Uwe
[-- Attachment #2: signature.asc --]
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^ permalink raw reply [flat|nested] 7+ messages in thread