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>

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 7206553..1edc830 100644 (file)
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -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);
-
-       /* Open source pin should not be driven to 0 */
-       if (!value && test_bit(FLAG_OPEN_SOURCE,  &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);
+       }
 
-       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;
 }
 
 /**

diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index bee976f..50882e0 100644 (file)
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -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);