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

[David Riley]

Hi Sebastian,

Thanks for the feedback.

On Tue, Aug 26, 2014 at 6:43 PM, Sebastian Reichel <sre@xxxxxxxxxx> wrote:
> 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).

Fixed.

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

>> +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.

>> +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.

>
>> +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.

>
>> +Examples:
>> +
>> +gpio-restart {
>> +     compatible = "gpio-restart";
>> +     gpios = <&gpio 4 0>;
>> +     priority = /bits/ 8 <200>;
>> +};
>> [...]
>
> -- Sebastian
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/