NAME

       fdt_pinctrl — FDT I/O pin multiplexing support

SYNOPSIS

       device fdt_pinctrl

DESCRIPTION

       Pin  multiplexing  is  a  technology  used  to re-purpose a single physical connection (depending on chip
       packaging it may be pin, ball, or pad) by routing its signal to any one of several different SoC internal
       devices.  For example, based on the actual device design, a single SoC chip  pin  might  perform  any  of
       these roles: SPI clock, I2C data, GPIO pin, or PWM signal.  Function selection is performed by the pinmux
       controller,  a  SoC  hardware block which is usually controlled by a set of registers.  Pinmux controller
       capabilities and register format depend on the actual hardware implementation.

       On fdt(4) based systems, the pinmux controller is represented by a node in the device tree.  It may  have
       any  number of child nodes representing pin configuration groups.  Properties of such nodes are hardware-
       specific and handled by individual pinctrl drivers.

   Example 1
       Pinmux controller device tree node

       pinctrl@7e220000 {
           compatible = "vndr,soc1715-pinctrl";
           reg = <0x7e220000 0x100>

           spi0_pins: spi0 {
               vndr,pins = <11 12>
               vndr,functions = <ALT0 ALT5>
           }

           i2c0_pins: i2c0 {
               ...
           }
       }

       Client devices are hardware devices  that  require  certain  pin  configurations  to  function  properly.
       Depending  on  the  state  the device is in (active, idle) it might require different pin configurations.
       Each configuration is described by setting the pinctrl-N property to the list  of  phandles  pointing  to
       specific  child  nodes  of  the  pinmux  controller  node.   N  is  an  integer value starting with 0 and
       incremented by 1 for every new set of pin configurations.  pinctrl-0 is a default configuration  that  is
       applied  in  the  fdt_pinctrl_configure_tree(9)  call.  In addition to referring to pin configurations by
       index, they can be referred to by name if the pinctrl-names property is set.  The value of  pinctrl-names
       is  a  list  of  strings  with  names  for  each pinctrl-N property.  Client devices can request specific
       configuration using fdt_pinctrl_configure(9) and fdt_pinctrl_configure_by_name(9).

   Example 2
       backlight@7f000000 {
           compatible = "vndr,vndr-bl"
           reg = <0x7f000000 0x20>
           ...
           pinctrl-name = "active", "idle"
           pinctrl-0 = <&backlight_active_pins>
           pinctrl-1 = <&backlight_idle_pins>
       }

       The pinctrl  driver  should  implement  the  FDT_PINCTRL_CONFIGURE  method,  register  itself  as  a  pin
       configuration handler by calling fdt_pinctrl_register function, and call fdt_pinctrl_configure_tree(9) to
       configure pins for all enabled devices (devices where the "status" property is not set to "disabled").

SEE ALSO

       fdt_pinctrl(9)

HISTORY

       The fdt_pinctrl driver first appeared in FreeBSD 10.2.

AUTHORS

       The  fdt_pinctrl  device  driver  was  developed  by  Ian Lepore <ian@FreeBSD.org>.  This manual page was
       written by Oleksandr Tymoshenko <gonzo@FreeBSD.org>.

Debian                                            March 3, 2018                                   FDT_PINCTRL(4)