Hi,
On Tue, Aug 26, 2014 at 4:45 PM, David Riley <davidriley@xxxxxxxxxxxx> wrote:
> This driver registers a restart handler to set a GPIO line high/low
> to reset a board based on devicetree bindings.
>
> Signed-off-by: David Riley <davidriley@xxxxxxxxxxxx>
> ---
> .../devicetree/bindings/gpio/gpio-restart.txt | 48 +++++++
> drivers/power/reset/Kconfig | 8 ++
> drivers/power/reset/Makefile | 1 +
> drivers/power/reset/gpio-restart.c | 142 +++++++++++++++++++++
> 4 files changed, 199 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/gpio/gpio-restart.txt
> create mode 100644 drivers/power/reset/gpio-restart.c
>
> 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.
> +
> +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. If the optional properties 'input' is
> +not found, the GPIO line will be driven in the inactive state.
> +Otherwise its configured as an input.
> +
> +When do_kernel_restart is called the various restart handlers will be tried
> +in order.
The above sentence documents the kernel behavior, not the hardware
description/binding.
> +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.
It's possible that this behavior is inadequate for some hardware in
the future -- if so they can amend the binding (i.e. this comment is
an attempt at preemptive bikeshed avoidance :)
> +
> +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.
Isn't this the same as configuring the pin as tristate? I think that
should probably be controlled by pinmux setup instead?
> +- 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
This is sort of leaking linux implementation, but it's also a useful
feature to have in the description. It seems sane enough to me to use.
> +
> +Examples:
> +
> +gpio-restart {
> + compatible = "gpio-restart";
> + gpios = <&gpio 4 0>;
> + priority = /bits/ 8 <200>;
I think it makes sense to just have this as a regular cell instead of
doing an 8-bit value -- it's how we normally handle these elsewhere.
-Olof
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