drivers/gpio: Add a driver that wraps the PWM API as a GPIO controller

For cases where spare PWM outputs are available, but are desired
to be addressed a standard outputs instead.
Wraps a PWM channel as a new GPIO chip with the one output.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index b2d4ffa..addea3a 100644 (file)
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -485,6 +485,14 @@ config GPIO_PMIC_EIC_SPRD
        help
          Say yes here to support Spreadtrum PMIC EIC device.
 
+config GPIO_PWM
+       tristate "PWM chip GPIO"
+       depends on OF_GPIO
+       depends on PWM
+       help
+         Turn on support for exposing a PWM chip as a GPIO
+         driver.
+
 config GPIO_PXA
        bool "PXA GPIO support"
        depends on ARCH_PXA || ARCH_MMP || COMPILE_TEST

diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index 0900302..0980f9b 100644 (file)
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -121,6 +121,7 @@ obj-$(CONFIG_GPIO_PCI_IDIO_16)              += gpio-pci-idio-16.o
 obj-$(CONFIG_GPIO_PISOSR)              += gpio-pisosr.o
 obj-$(CONFIG_GPIO_PL061)               += gpio-pl061.o
 obj-$(CONFIG_GPIO_PMIC_EIC_SPRD)       += gpio-pmic-eic-sprd.o
+obj-$(CONFIG_GPIO_PWM)                 += gpio-pwm.o
 obj-$(CONFIG_GPIO_PXA)                 += gpio-pxa.o
 obj-$(CONFIG_GPIO_RASPBERRYPI_EXP)     += gpio-raspberrypi-exp.o
 obj-$(CONFIG_GPIO_RC5T583)             += gpio-rc5t583.o

diff --git a/drivers/gpio/gpio-pwm.c b/drivers/gpio/gpio-pwm.c
new file mode 100644 (file)
index 0000000..89f5d6b
--- /dev/null
+++ b/drivers/gpio/gpio-pwm.c
@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * GPIO driver wrapping PWM API
+ *
+ * PWM 0% and PWM 100% are equivalent to digital GPIO
+ * outputs, and there are times where it is useful to use
+ * PWM outputs as straight GPIOs (eg outputs of NXP PCA9685
+ * I2C PWM chip). This driver wraps the PWM API as a GPIO
+ * controller.
+ *
+ * Copyright (C) 2021 Raspberry Pi (Trading) Ltd.
+ */
+
+#include <linux/err.h>
+#include <linux/gpio/driver.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/pwm.h>
+
+struct pwm_gpio {
+       struct gpio_chip gc;
+       struct pwm_device **pwm;
+};
+
+static int pwm_gpio_get_direction(struct gpio_chip *gc, unsigned int off)
+{
+       return GPIO_LINE_DIRECTION_OUT;
+}
+
+static void pwm_gpio_set(struct gpio_chip *gc, unsigned int off, int val)
+{
+       struct pwm_gpio *pwm_gpio = gpiochip_get_data(gc);
+       struct pwm_state state;
+
+       pwm_get_state(pwm_gpio->pwm[off], &state);
+       state.duty_cycle = val ? state.period : 0;
+       pwm_apply_state(pwm_gpio->pwm[off], &state);
+}
+
+static int pwm_gpio_parse_dt(struct pwm_gpio *pwm_gpio,
+                            struct device *dev)
+{
+       struct device_node *node = dev->of_node;
+       struct pwm_state state;
+       int ret = 0, i, num_gpios;
+       const char *pwm_name;
+
+       if (!node)
+               return -ENODEV;
+
+       num_gpios = of_property_count_strings(node, "pwm-names");
+       if (num_gpios <= 0)
+               return 0;
+
+       pwm_gpio->pwm = devm_kzalloc(dev,
+                                    sizeof(*pwm_gpio->pwm) * num_gpios,
+                                    GFP_KERNEL);
+       if (!pwm_gpio->pwm)
+               return -ENOMEM;
+
+       for (i = 0; i < num_gpios; i++) {
+               ret = of_property_read_string_index(node, "pwm-names", i,
+                                                   &pwm_name);
+               if (ret) {
+                       dev_err(dev, "unable to get pwm device index %d, name %s",
+                               i, pwm_name);
+                       goto error;
+               }
+
+               pwm_gpio->pwm[i] = devm_pwm_get(dev, pwm_name);
+               if (IS_ERR(pwm_gpio->pwm[i])) {
+                       ret = PTR_ERR(pwm_gpio->pwm[i]);
+                       if (ret != -EPROBE_DEFER)
+                               dev_err(dev, "unable to request PWM\n");
+                       goto error;
+               }
+
+               /* Sync up PWM state. */
+               pwm_init_state(pwm_gpio->pwm[i], &state);
+
+               state.duty_cycle = 0;
+               pwm_apply_state(pwm_gpio->pwm[i], &state);
+       }
+
+       pwm_gpio->gc.ngpio = num_gpios;
+
+error:
+       return ret;
+}
+
+static int pwm_gpio_probe(struct platform_device *pdev)
+{
+       struct device *dev = &pdev->dev;
+       struct pwm_gpio *pwm_gpio;
+       int ret;
+
+       pwm_gpio = devm_kzalloc(dev, sizeof(*pwm_gpio), GFP_KERNEL);
+       if (!pwm_gpio)
+               return -ENOMEM;
+
+       pwm_gpio->gc.parent = dev;
+       pwm_gpio->gc.label = "pwm-gpio";
+       pwm_gpio->gc.owner = THIS_MODULE;
+       pwm_gpio->gc.of_node = dev->of_node;
+       pwm_gpio->gc.base = -1;
+
+       pwm_gpio->gc.get_direction = pwm_gpio_get_direction;
+       pwm_gpio->gc.set = pwm_gpio_set;
+       pwm_gpio->gc.can_sleep = true;
+
+       ret = pwm_gpio_parse_dt(pwm_gpio, dev);
+       if (ret)
+               return ret;
+
+       if (!pwm_gpio->gc.ngpio)
+               return 0;
+
+       return devm_gpiochip_add_data(dev, &pwm_gpio->gc, pwm_gpio);
+}
+
+static int pwm_gpio_remove(struct platform_device *pdev)
+{
+       return 0;
+}
+
+static const struct of_device_id pwm_gpio_of_match[] = {
+       { .compatible = "pwm-gpio" },
+       { }
+};
+MODULE_DEVICE_TABLE(of, pwm_gpio_of_match);
+
+static struct platform_driver pwm_gpio_driver = {
+       .driver = {
+               .name           = "pwm-gpio",
+               .of_match_table = of_match_ptr(pwm_gpio_of_match),
+       },
+       .probe  = pwm_gpio_probe,
+       .remove = pwm_gpio_remove,
+};
+module_platform_driver(pwm_gpio_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Dave Stevenson <dave.stevenson@raspberrypi.com>");
+MODULE_DESCRIPTION("PWM GPIO driver");