Hi,
On Sun, Jun 15, 2014 at 03:11:29PM +0800, Houcheng Lin wrote:
> The Problem
> -----------
> The reset signal on a hardware board is send either:
> - during machine initialization
> - during bus master's initialization
>
> In some hardware design, devices on bus need a non-standard and extra reset
> signal after bus is initialied. Most reason is to wake up device from hanging
> state.
>
> The board spefic reset code can not be put into machine init code, as it is
> too early. This code can not also be put onto chip's driver, as it is board
> specific and not suitable for a common chip driver.
>
> Defer Reset Object
> ------------------
> The defer reset object is to resolve this issue, developer can put a defer-
> reset device on the board's dts file and enable DEFER RESET OBJECT CONFIG.
> During driver init-calls, a defer-reset object is created and issue reset signal
> after the enclosing device is initialized.
>
> This eliminate the need to rewrite a driver module with only one purpose: sending
> a board specific reset. This also allow mainstream kernel to support many boards
> that modify the common drivers to send board specific reset. Configuring defer-reset
> device in dts leave the board specific reset rules on board level and simple to
> maintain.
>
> Example dts File
> ----------------
> usb-ehci-chip@1211000{
> usb-phy = <&usb2_phy>;
> defer_reset_vbus {
> compatible = "defer-reset";
> reset-gpios = <&gpx3 5 1>;
> reset-init = <0>;
> reset-end = <1>;
> delay = <5>;
> };
> };
>
> Block Diagram of dts File
> -------------------------
> +-------------------------------------+
> | usb-ehci-chip@1211000 |
> | +-------------------------+ |
> | | defer-reset(gpx3) | |
> | +-------------------------+ |
> +-------------------------------------+
>
> Signed-off-by: Houcheng Lin <houcheng@xxxxxxxxx>
> ---
> .../devicetree/bindings/gpio/gpio-defer-reset.txt | 22 +++
> drivers/power/reset/Kconfig | 8 +
> drivers/power/reset/Makefile | 1 +
> drivers/power/reset/gpio-defer-reset.c | 192 +++++++++++++++++++++
I think this belongs to drivers/reset and not to drivers/power/reset.
The drivers in drivers/power/reset are about board reboot / shutdown.
This driver seems to be used for periphals.
> 4 files changed, 223 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/gpio/gpio-defer-reset.txt
> create mode 100644 drivers/power/reset/gpio-defer-reset.c
>
> diff --git a/Documentation/devicetree/bindings/gpio/gpio-defer-reset.txt b/Documentation/devicetree/bindings/gpio/gpio-defer-reset.txt
> new file mode 100644
> index 0000000..5d55830
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/gpio/gpio-defer-reset.txt
> @@ -0,0 +1,22 @@
> +GPIO defer reset binding
> +
> +Put a defer-reset device in a device node and enable DEFER RESET OBJECT CONFIG.
> +During driver init-calls, a defer-reset object will be created and issue reset
> +signal after the enclosing device node's initialization complete.
> +
> +Required properties:
> +- compatible:
> + - "defer-reset" for creating defer reset object
> +- reset-gpio: specify gpio pin, can be an array.
> +- reset-init: specify reset signal initial value, can be 0 or 1.
You can simply use GPIO's HIGH_ACTIVE / LOW_ACTIVE flag for the
"initial value".
> +- reset-end: specify reset signal end value, can be 0 or 1.
You can use a property without a value for booleans. If the property
is there, the value is 1 and if its missing the value is 0.
For example in your case you could use
hold-reset-line;
to inform the system, that the reset signal should not be changed
back after the specified time.
> +- delay: specify reset duration in ms.
Alternatively you could do this via the duration. An infinite long
reset signal basically means, that the line is never changed back.
> +
> +Example:
> + defer_reset_vbus {
> + compatible = "defer-reset";
> + reset-gpios = <&gpx3 5 1>;
> + reset-init = <0>;
> + reset-end = <1>;
> + delay = <5>;
> + };
To give a few examples for the above comments:
/* keep "gpx3 5" low for 5ms, change back to high afterwards */
defer_reset_vbus {
compatible = "defer-reset";
reset-gpios = <&gpx3 5 GPIO_ACTIVE_LOW>;
duration = <5>;
};
/* keep "gpx3 5" high for 5ms, change back to low afterwards */
defer_reset_vbus {
compatible = "defer-reset";
reset-gpios = <&gpx3 5 GPIO_ACTIVE_HIGH>;
duration = <5>;
};
/* keep "gpx3 5" low */
defer_reset_vbus {
compatible = "defer-reset";
reset-gpios = <&gpx3 5 GPIO_ACTIVE_LOW>;
duration = <0>;
};
> [...]
-- Sebastian
Attachment:
signature.asc
Description: Digital signature
