This is just a suggestion up to now, I don't have any code yet to share.
Apart from minor rewording to make the document easier to understand and
less ambiguous the relevant changes are:
- add an "enable-gpio" property.
I admit the device I'm currently working with doesn't have this.
Still I imagine this to be a common hardware property. I added it
mainly to demonstrate the shortcomings of the existing binding.
- rename "gpios" to "trigger-gpio"
This is more descriptive. And given there is "enable-gpio" now, too,
using plain "gpios" seems wrong.
- deprecate always-running
Apart from the description describing the driver behaviour and not
the device property, always-running only seems to make sense in
combination with hw_algo = "level" and in reality should only
invalidate the sentence: "The watchdog timer is disabled when GPIO is
left floating or connected to a three-state buffer."
With this semantic using a property "disable-on-tri-state" sounds
more sensible. And note that even the following would make sense
hardware-wise, while the device tree looks stupid:
watchdog {
compatible = "linux,wdt-gpio";
trigger-gpio = ...;
hw_algo = "toggle";
always-running;
enable-gpio = ...;
};
(i.e. always-running, but disable possible by a dedicated gpio.)
I'm aware that using ...-gpios is more common than ...-gpio. I don't
feel strong here, but as only a single gpio makes sense here, having
-gpios seems wrong.
Also I considered renaming hw_margin_ms and hw_algo to use - instead of
_. Doing this might even ease to implement the changes above in a
compatible way. I.e. assume the watchdog can be disabled by tristating
the gpio if the description uses underscores instead of hyphen.
Feedback very welcome!
Best regards
Uwe
---
.../devicetree/bindings/watchdog/gpio-wdt.txt | 37 ++++++++++++++--------
1 file changed, 23 insertions(+), 14 deletions(-)
diff --git a/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt b/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt
index 198794963786..ceb1a5f95f44 100644
--- a/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt
+++ b/Documentation/devicetree/bindings/watchdog/gpio-wdt.txt
@@ -2,27 +2,36 @@
Required Properties:
- compatible: Should contain "linux,wdt-gpio".
-- gpios: From common gpio binding; gpio connection to WDT reset pin.
-- hw_algo: The algorithm used by the driver. Should be one of the
+- trigger-gpio: reference to the gpio connected to watchdog's input pin
+ (typically called WDI).
+- hw_algo: The algorithm used by the device. Should be one of the
following values:
- - toggle: Either a high-to-low or a low-to-high transition clears
- the WDT counter. The watchdog timer is disabled when GPIO is
- left floating or connected to a three-state buffer.
- - level: Low or high level starts counting WDT timeout,
- the opposite level disables the WDT. Active level is determined
- by the GPIO flags.
-- hw_margin_ms: Maximum time to reset watchdog circuit (milliseconds).
+ - toggle: Both a high-to-low and a low-to-high transition clear
+ the watchdog counter.
+ - level: Low or high level starts counting watchdog timeout,
+ the opposite level disables the watchdog. Active level is determined
+ by the GPIO flags of the trigger-gpio (with active meaning the watchdog is
+ enabled).
+- hw_margin_ms: Maximum time to reset watchdog circuit in milliseconds.
Optional Properties:
-- always-running: If the watchdog timer cannot be disabled, add this flag to
- have the driver keep toggling the signal without a client. It will only cease
- to toggle the signal when the device is open and the timeout elapsed.
+- enable-gpio: Reference to a gpio that when inactive stops the watchdog.
+- disable-on-tri-state: property that signals that the watchdog can be stopped
+ by setting the trigger-gpio to tri-state.
+
+Deprecated Properties:
+- always-running: This property signals the watchdog timer cannot be disabled.
+ Without this property the watchdog is expected to turn off for hw_algo=toggle
+ watchdogs when the gpio is set to tri-state.
+ Don't use it for new device descriptions as it is misleading in the presence
+ of an enable-gpio.
+- gpios: deprecated alias of trigger-gpio
Example:
watchdog: watchdog {
/* ADM706 */
- compatible = "linux,wdt-gpio";
- gpios = <&gpio3 9 GPIO_ACTIVE_LOW>;
+ compatible = "adi,adm706", "linux,wdt-gpio";
+ trigger-gpio = <&gpio3 9 GPIO_ACTIVE_LOW>;
hw_algo = "toggle";
hw_margin_ms = <1600>;
};
--
2.1.4
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