drivers/pinctrl: Add the concept of an "init" state

For pinctrl the "default" state is applied to pins before the driver's
probe function is called.  This is normally a sensible thing to do,
but in some cases can cause problems.  That's because the pins will
change state before the driver is given a chance to program how those
pins should behave.

As an example you might have a regulator that is controlled by a PWM
(output high = high voltage, output low = low voltage).  The firmware
might leave this pin as driven high.  If we allow the driver core to
reconfigure this pin as a PWM pin before the PWM's probe function runs
then you might end up running at too low of a voltage while we probe.

Let's introudce a new "init" state.  If this is defined we'll set
pinctrl to this state before probe and then "default" after probe
(unless the driver explicitly changed states already).

An alternative idea that was thought of was to use the pre-existing
"sleep" or "idle" states and add a boolean property that we should
start in that mode.  This was not done because the "init" state is
needed for correctness and those other states are only present (and
only transitioned in to and out of) when (optional) power management
is enabled.

Changes in v3:
- Moved declarations to pinctrl/devinfo.h
- Fixed author/SoB

Changes in v2:
- Added comment to pinctrl_init_done() as per Linus W.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Tested-by: Caesar Wang <wxt@rock-chips.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/pinctrl/devinfo.h b/include/linux/pinctrl/devinfo.h
index 281cb91ddcf5..05082e407c4a 100644
--- a/include/linux/pinctrl/devinfo.h
+++ b/include/linux/pinctrl/devinfo.h
@@ -24,10 +24,14 @@
  * struct dev_pin_info - pin state container for devices
  * @p: pinctrl handle for the containing device
  * @default_state: the default state for the handle, if found
+ * @init_state: the state at probe time, if found
+ * @sleep_state: the state at suspend time, if found
+ * @idle_state: the state at idle (runtime suspend) time, if found
  */
 struct dev_pin_info {
 	struct pinctrl *p;
 	struct pinctrl_state *default_state;
+	struct pinctrl_state *init_state;
 #ifdef CONFIG_PM
 	struct pinctrl_state *sleep_state;
 	struct pinctrl_state *idle_state;
@@ -35,6 +39,7 @@ struct dev_pin_info {
 };
 
 extern int pinctrl_bind_pins(struct device *dev);
+extern int pinctrl_init_done(struct device *dev);
 
 #else
 
@@ -45,5 +50,10 @@ static inline int pinctrl_bind_pins(struct device *dev)
 	return 0;
 }
 
+static inline int pinctrl_init_done(struct device *dev)
+{
+	return 0;
+}
+
 #endif /* CONFIG_PINCTRL */
 #endif /* PINCTRL_DEVINFO_H */