Re: [PATCH v1 1/1] power: Add simple gpio-restart driver

From: Sebastian Reichel
Date: Tue Aug 26 2014 - 21:43:20 EST

Hi David,

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

> [...]
> 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).

> [...]
> +
> +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).

> +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?

> +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

> +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).

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

-- Sebastian

Attachment: signature.asc
Description: Digital signature