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>

2 files changed, 15 insertions, 2 deletions

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index be0eb4639128..a641cf3ccad6 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -322,6 +322,8 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 			goto probe_failed;
 	}
 
+	pinctrl_init_done(dev);
+
 	if (dev->pm_domain && dev->pm_domain->sync)
 		dev->pm_domain->sync(dev);
 
diff --git a/drivers/base/pinctrl.c b/drivers/base/pinctrl.c
index 5fb74b43848e..076297592754 100644
--- a/drivers/base/pinctrl.c
+++ b/drivers/base/pinctrl.c
@@ -42,9 +42,20 @@ int pinctrl_bind_pins(struct device *dev)
 		goto cleanup_get;
 	}
 
-	ret = pinctrl_select_state(dev->pins->p, dev->pins->default_state);
+	dev->pins->init_state = pinctrl_lookup_state(dev->pins->p,
+					PINCTRL_STATE_INIT);
+	if (IS_ERR(dev->pins->init_state)) {
+		/* Not supplying this state is perfectly legal */
+		dev_dbg(dev, "no init pinctrl state\n");
+
+		ret = pinctrl_select_state(dev->pins->p,
+					   dev->pins->default_state);
+	} else {
+		ret = pinctrl_select_state(dev->pins->p, dev->pins->init_state);
+	}
+
 	if (ret) {
-		dev_dbg(dev, "failed to activate default pinctrl state\n");
+		dev_dbg(dev, "failed to activate initial pinctrl state\n");
 		goto cleanup_get;
 	}