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>.