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Commit c663e5f5 authored by Linus Walleij's avatar Linus Walleij
Browse files

gpio: support native single-ended hardware drivers 



Some GPIO controllers has a special hardware bit we can flip
to support open drain / source. This means that on these hardwares
we do not need to emulate OD/OS by setting the line to input
instead of actively driving it high/low. Add an optional vtable
callback to the driver set_single_ended() so that driver can
implement this in hardware if they have it.

We may need a pinctrl_gpio_set_config() call at some point to
propagate this down to a backing pin control device on systems
with split GPIO/pin control.

Reported-by: default avatarMichael Hennerich <michael.hennerich@analog.com>
Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
parent 6e66a659

drivers/gpio/gpiolib.c

+37 −15
Original line number Diff line number Diff line
@@ -1509,8 +1509,8 @@ EXPORT_SYMBOL_GPL(gpiod_direction_input); 


static int _gpiod_direction_output_raw(struct gpio_desc *desc, int value)

{

	struct gpio_chip	*chip;

	int			status = -EINVAL;

	struct gpio_chip *gc = desc->gdev->chip;

	int ret;



	/* GPIOs used for IRQs shall not be set as output */

	if (test_bit(FLAG_USED_AS_IRQ, &desc->flags)) {
@@ -1520,28 +1520,50 @@ static int _gpiod_direction_output_raw(struct gpio_desc *desc, int value) 
		return -EIO;

	}



	/* Open drain pin should not be driven to 1 */

	if (value && test_bit(FLAG_OPEN_DRAIN,  &desc->flags))

	if (test_bit(FLAG_OPEN_DRAIN, &desc->flags)) {

		/* First see if we can enable open drain in hardware */

		if (gc->set_single_ended) {

			ret = gc->set_single_ended(gc, gpio_chip_hwgpio(desc),

						   LINE_MODE_OPEN_DRAIN);

			if (!ret)

				goto set_output_value;

		}

		/* Emulate open drain by not actively driving the line high */

		if (value)

			return gpiod_direction_input(desc);



	/* Open source pin should not be driven to 0 */

	if (!value && test_bit(FLAG_OPEN_SOURCE,  &desc->flags))

	}

	else if (test_bit(FLAG_OPEN_SOURCE, &desc->flags)) {

		if (gc->set_single_ended) {

			ret = gc->set_single_ended(gc, gpio_chip_hwgpio(desc),

						   LINE_MODE_OPEN_SOURCE);

			if (!ret)

				goto set_output_value;

		}

		/* Emulate open source by not actively driving the line low */

		if (!value)

			return gpiod_direction_input(desc);

	} else {

		/* Make sure to disable open drain/source hardware, if any */

		if (gc->set_single_ended)

			gc->set_single_ended(gc,

					     gpio_chip_hwgpio(desc),

					     LINE_MODE_PUSH_PULL);

	}



	chip = desc->gdev->chip;

	if (!chip->set || !chip->direction_output) {

set_output_value:

	if (!gc->set || !gc->direction_output) {

		gpiod_warn(desc,

		       "%s: missing set() or direction_output() operations\n",

		       __func__);

		return -EIO;

	}



	status = chip->direction_output(chip, gpio_chip_hwgpio(desc), value);

	if (status == 0)

	ret = gc->direction_output(gc, gpio_chip_hwgpio(desc), value);

	if (!ret)

		set_bit(FLAG_IS_OUT, &desc->flags);

	trace_gpio_value(desc_to_gpio(desc), 0, value);

	trace_gpio_direction(desc_to_gpio(desc), 0, status);

	return status;

	trace_gpio_direction(desc_to_gpio(desc), 0, ret);

	return ret;

}



/**

include/linux/gpio/driver.h

+24 −1
Original line number Diff line number Diff line
@@ -19,6 +19,18 @@ struct gpio_device; 


#ifdef CONFIG_GPIOLIB



/**

 * enum single_ended_mode - mode for single ended operation

 * @LINE_MODE_PUSH_PULL: normal mode for a GPIO line, drive actively high/low

 * @LINE_MODE_OPEN_DRAIN: set line to be open drain

 * @LINE_MODE_OPEN_SOURCE: set line to be open source

 */

enum single_ended_mode {

	LINE_MODE_PUSH_PULL,

	LINE_MODE_OPEN_DRAIN,

	LINE_MODE_OPEN_SOURCE,

};



/**

 * struct gpio_chip - abstract a GPIO controller

 * @label: a functional name for the GPIO device, such as a part
@@ -39,6 +51,14 @@ struct gpio_device; 
 * @set_multiple: assigns output values for multiple signals defined by "mask"

 * @set_debounce: optional hook for setting debounce time for specified gpio in

 *	interrupt triggered gpio chips

 * @set_single_ended: optional hook for setting a line as open drain, open

 *	source, or non-single ended (restore from open drain/source to normal

 *	push-pull mode) this should be implemented if the hardware supports

 *	open drain or open source settings. The GPIOlib will otherwise try

 *	to emulate open drain/source by not actively driving lines high/low

 *	if a consumer request this. The driver may return -ENOTSUPP if e.g.

 *	it supports just open drain but not open source and is called

 *	with LINE_MODE_OPEN_SOURCE as mode argument.

 * @to_irq: optional hook supporting non-static gpio_to_irq() mappings;

 *	implementation may not sleep

 * @dbg_show: optional routine to show contents in debugfs; default code
@@ -130,6 +150,9 @@ struct gpio_chip { 
	int			(*set_debounce)(struct gpio_chip *chip,

						unsigned offset,

						unsigned debounce);

	int			(*set_single_ended)(struct gpio_chip *chip,

						unsigned offset,

						enum single_ended_mode mode);



	int			(*to_irq)(struct gpio_chip *chip,

						unsigned offset);