Hi Sebastian,

Thanks for the feedback.

On Tue, Aug 26, 2014 at 6:43 PM, Sebastian Reichel [off-list ref] wrote:

Hi David,

On Tue, Aug 26, 2014 at 04:45:05PM -0700, David Riley wrote:

quoted

This driver registers a restart handler to set a GPIO line high/low
to reset a board based on devicetree bindings.

Driver looks fine to me. I have some comments about the
Documentation, though:

quoted

[...]

diff --git a/Documentation/devicetree/bindings/gpio/gpio-restart.txt b/Documentation/devicetree/bindings/gpio/gpio-restart.txt
new file mode 100644
index 0000000..7cd58788
--- /dev/null
+++ b/Documentation/devicetree/bindings/gpio/gpio-restart.txt

@@ -0,0 +1,48 @@
+Driver a GPIO line that can be used to restart the system as a
+restart handler.

Please fix the Typo (first word).

Fixed.

quoted

[...]
+
+The driver supports both level triggered and edge triggered power off.
+At driver load time, the driver will request the given gpio line and
+install a restart handler.

The wording is too driver centric IMHO. You are supposed to document
the binding in a generic way. Maybe start with something like:

"This binding supports level and edge triggered reset."

(power off is the wrong word, since there is already gpio-poweroff).

I've cleaned this up for v2.

quoted

+If the optional properties 'input' is +not found, the GPIO line
+will be driven in the inactive state. Otherwise its configured
+as an input.

What is this needed for?

This allows other hardware to be attached to the same line to reset
the system.  Carried forward from the gpio-poweroff implementation I
based this on.

quoted

+When do_kernel_restart is called the various restart handlers will be tried
+in order.  The gpio is configured as an output, and drive active, so
+triggering a level triggered power off condition. This will also cause an
+inactive->active edge condition, so triggering positive edge triggered
+power off. After a delay of 100ms, the GPIO is set to inactive, thus
+causing an active->inactive edge, triggering negative edge triggered power
+off. After another 100ms delay the GPIO is driver active again. If the
+power is still on and the CPU still running after a 3000ms delay, a
+WARN_ON(1) is emitted.

I really appreciate the description of the driver (it made it easier
to review it :)), but Documentation/devicetree should avoid
Linuxisms. In other words: this is the wrong location for the
description.

I've cleaned this up as well and made the explicit delays configurable.

quoted

+Required properties:
+- compatible : should be "gpio-restart".
+- gpios : The GPIO to set high/low, see "gpios property" in
+  Documentation/devicetree/bindings/gpio/gpio.txt. If the pin should be
+  low to power down the board set it to "Active Low", otherwise set
+  gpio to "Active High".
+
+Optional properties:
+- input : Initially configure the GPIO line as an input. Only reconfigure
+  it to an output when the machine_restart function is called. If this optional
+  property is not specified, the GPIO is initialized as an output in its
+  inactive state.
+- priority : A priority ranging from 0 to 255 (default 128) according to
+  the following guidelines:
+     0:      Restart handler of last resort, with limited restart
+             capabilities
+     128:    Default restart handler; use if no other restart handler is
+             expected to be available, and/or if restart functionality is
+             sufficient to restart the entire system
+     255:    Highest priority restart handler, will preempt all other
+             restart handlers

You should add a short information about the property type here
(e.g. "8 bit integer" for priority).

As per Olof's comments I've just changed this to be a regular cell for
consistency with other bindings and will handle the range checking
internally.

quoted

+Examples:
+
+gpio-restart {
+     compatible = "gpio-restart";
+     gpios = <&gpio 4 0>;
+     priority = /bits/ 8 <200>;
+};
[...]

-- Sebastian