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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: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
This commit is contained in:
Linus Walleij 2016-03-22 10:51:16 +01:00
parent 6e66a6599a
commit c663e5f567
2 changed files with 61 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

52
drivers/gpio/gpiolib.c
View File

@ -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))
return gpiod_direction_input(desc);
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);
}
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);
}
/* Open source pin should not be driven to 0 */
if (!value && test_bit(FLAG_OPEN_SOURCE, &desc->flags))
return gpiod_direction_input(desc);
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;
}
/**

25
include/linux/gpio/driver.h
View File

@ -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
@ -38,7 +50,15 @@ struct gpio_device;
* @set: assigns output value for signal "offset"
* @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
* 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);