Hi Uwe,
On Wed, Jul 13, 2016 at 6:01 AM, Uwe Kleine-König
<u.kleine-koenig@xxxxxxxxxxxxxx> wrote:
> A part of my machine looks as follows (simplified):
>
> ,------------------------.
> | ,---------. |
> | | imx25 o--RX----◁---o---
> | | o--GPIO--' |
> | `---------' |
> `------------------------'
>
> that is, there is a driver on the RX line that must be enabled before
> the UART can be used. (That is necessary because the default mux of the
> RX pad after reset is an output.)
>
> To represent this in the device tree I do:
>
> pinctrl_uart5: uart5 {
> fsl,pins = <
> ...
> MX25_PAD_LBA__UART5_RXD 0x00000000
> MX25_PAD_CS5__GPIO_3_21 0x00002001
> ...
> };
>
> &uart5 {
> pinctrl-names = "default";
> pinctrl-0 = <&pinctrl_uart5>;
>
> enable-gpio = <&gpio3 21 GPIO_ACTIVE_LOW>;
> ...
> };
>
> This way it's ensured that the gpio is only enabled when the LBA pad is
> muxed as RX (together with the bootloader that sets the GPIO high).
>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Since this is not imx serial specific it could be made more generic.
What about extending
Documentation/devicetree/bindings/serial/slave-device.txt to handle
this GPIO, or maybe a regulator?
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