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>

1 files changed, 24 insertions, 1 deletions

diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index bee976f82788..50882e09289b 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -20,6 +20,18 @@ 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
  *      number or the name of the SoC IP-block implementing it.
@@ -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);