[PATCH 2/4] pinctrl: Add skew-delay pin config and bindings

Linus Walleij
2017-10-28T13:37:17Z

Some pin controllers (such as the Gemini) can control the
expected clock skew and output delay on certain pins with a
sub-nanosecond granularity. This is typically done by shunting
in a number of double inverters in front of or behind the pin.
Make it possible to configure this with a generic binding.

Cc: devicetree at vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt | 4 ++++
drivers/pinctrl/pinconf-generic.c | 2 ++
include/linux/pinctrl/pinconf-generic.h | 5 +++++
3 files changed, 11 insertions(+)

diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
index 4483cc31e531..ad9bbbba36e9 100644
--- a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
+++ b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
@@ -271,6 +271,10 @@ output-high - set the pin to output mode with high level
sleep-hardware-state - indicate this is sleep related state which will be programmed
into the registers for the sleep state.
slew-rate - set the slew rate
+skew-delay - this affects the expected clock skew on input pins
+ and the delay before latching a value to an output
+ pin. Typically indicates how many double-inverters are
+ used to delay the signal.

For example:

diff --git a/drivers/pinctrl/pinconf-generic.c b/drivers/pinctrl/pinconf-generic.c
index 8eaa25c3384f..b4f7f8a458ea 100644
--- a/drivers/pinctrl/pinconf-generic.c
+++ b/drivers/pinctrl/pinconf-generic.c
@@ -49,6 +49,7 @@ static const struct pin_config_item conf_items[] = {
PCONFDUMP(PIN_CONFIG_POWER_SOURCE, "pin power source", "selector", true),
PCONFDUMP(PIN_CONFIG_SLEEP_HARDWARE_STATE, "sleep hardware state", NULL, false),
PCONFDUMP(PIN_CONFIG_SLEW_RATE, "slew rate", NULL, true),
+ PCONFDUMP(PIN_CONFIG_SKEW_DELAY, "skew delay", NULL, true),
};

static void pinconf_generic_dump_one(struct pinctrl_dev *pctldev,
@@ -181,6 +182,7 @@ static const struct pinconf_generic_params dt_params[] = {
{ "power-source", PIN_CONFIG_POWER_SOURCE, 0 },
{ "sleep-hardware-state", PIN_CONFIG_SLEEP_HARDWARE_STATE, 0 },
{ "slew-rate", PIN_CONFIG_SLEW_RATE, 0 },
+ { "skew-delay", PIN_CONFIG_SKEW_DELAY, 0 },
};

/**
diff --git a/include/linux/pinctrl/pinconf-generic.h b/include/linux/pinctrl/pinconf-generic.h
index 5d8bc7f21c2a..ec6dadcc1fde 100644
--- a/include/linux/pinctrl/pinconf-generic.h
+++ b/include/linux/pinctrl/pinconf-generic.h
@@ -90,6 +90,10 @@
* @PIN_CONFIG_SLEW_RATE: if the pin can select slew rate, the argument to
* this parameter (on a custom format) tells the driver which alternative
* slew rate to use.
+ * @PIN_CONFIG_SKEW_DELAY: if the pin has programmable skew rate (on inputs)
+ * or latch delay (on outputs) this parameter (in a custom format)
+ * specifies the clock skew or latch delay. It typically controls how
+ * many double inverters are put in front of the line.
* @PIN_CONFIG_END: this is the last enumerator for pin configurations, if
* you need to pass in custom configurations to the pin controller, use
* PIN_CONFIG_END+1 as the base offset.
@@ -117,6 +121,7 @@ enum pin_config_param {
PIN_CONFIG_POWER_SOURCE,
PIN_CONFIG_SLEEP_HARDWARE_STATE,
PIN_CONFIG_SLEW_RATE,
+ PIN_CONFIG_SKEW_DELAY,
PIN_CONFIG_END = 0x7F,
PIN_CONFIG_MAX = 0xFF,
};
--
2.13.6