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, 8 insertions, 0 deletions

diff --git a/include/linux/pinctrl/pinctrl-state.h b/include/linux/pinctrl/pinctrl-state.h
index b5919f8e6d1a..23073519339f 100644
--- a/include/linux/pinctrl/pinctrl-state.h
+++ b/include/linux/pinctrl/pinctrl-state.h
@@ -9,6 +9,13 @@
  *	hogs to configure muxing and pins at boot, and also as a state
  *	to go into when returning from sleep and idle in
  *	.pm_runtime_resume() or ordinary .resume() for example.
+ * @PINCTRL_STATE_INIT: normally the pinctrl will be set to "default"
+ *	before the driver's probe() function is called.  There are some
+ *	drivers where that is not appropriate becausing doing so would
+ *	glitch the pins.  In those cases you can add an "init" pinctrl
+ *	which is the state of the pins before drive probe.  After probe
+ *	if the pins are still in "init" state they'll be moved to
+ *	"default".
  * @PINCTRL_STATE_IDLE: the state the pinctrl handle shall be put into
  *	when the pins are idle. This is a state where the system is relaxed
  *	but not fully sleeping - some power may be on but clocks gated for
@@ -20,5 +27,6 @@
  *	ordinary .suspend() function.
  */
 #define PINCTRL_STATE_DEFAULT "default"
+#define PINCTRL_STATE_INIT "init"
 #define PINCTRL_STATE_IDLE "idle"
 #define PINCTRL_STATE_SLEEP "sleep"