NVIDIA Tegra20 pinmux controller

Required properties:
- compatible: "nvidia,tegra20-pinmux"
- reg: Should contain the register physical address and length for each of
  the tri-state, mux, pull-up/down, and pad control register sets.

Please refer to pinctrl-bindings.txt in this directory for details of the
common pinctrl bindings used by client devices, including the meaning of the
phrase "pin configuration node".

Tegra's pin configuration nodes act as a container for an abitrary number of
subnodes. Each of these subnodes represents some desired configuration for a
pin, a group, or a list of pins or groups. This configuration can include the
mux function to select on those pin(s)/group(s), and various pin configuration
parameters, such as pull-up, tristate, drive strength, etc.

The name of each subnode is not important; all subnodes should be enumerated
and processed purely based on their content.

Each subnode only affects those parameters that are explicitly listed. In
other words, a subnode that lists a mux function but no pin configuration
parameters implies no information about any pin configuration parameters.
Similarly, a pin subnode that describes a pullup parameter implies no
information about e.g. the mux function or tristate parameter. For this
reason, even seemingly boolean values are actually tristates in this binding:
unspecified, off, or on. Unspecified is represented as an absent property,
and off/on are represented as integer values 0 and 1.

Required subnode-properties:
- nvidia,pins : An array of strings. Each string contains the name of a pin or
    group. Valid values for these names are listed below.

Optional subnode-properties:
- nvidia,function: A string containing the name of the function to mux to the
  pin or group. Valid values for function names are listed below. See the Tegra
  TRM to determine which are valid for each pin or group.
- nvidia,pull: Integer, representing the pull-down/up to apply to the pin.
    0: none, 1: down, 2: up.
- nvidia,tristate: Integer.
    0: drive, 1: tristate.
- nvidia,high-speed-mode: Integer. Enable high speed mode the pins.
    0: no, 1: yes.
- nvidia,schmitt: Integer. Enables Schmitt Trigger on the input.
    0: no, 1: yes.
- nvidia,low-power-mode: Integer. Valid values 0-3. 0 is least power, 3 is
    most power. Controls the drive power or current. See "Low Power Mode"
    or "LPMD1" and "LPMD0" in the Tegra TRM.
- nvidia,pull-down-strength: Integer. Controls drive strength. 0 is weakest.
    The range of valid values depends on the pingroup. See "CAL_DRVDN" in the
    Tegra TRM.
- nvidia,pull-up-strength: Integer. Controls drive strength. 0 is weakest.
    The range of valid values depends on the pingroup. See "CAL_DRVUP" in the
    Tegra TRM.
- nvidia,slew-rate-rising: Integer. Controls rising signal slew rate. 0 is
    fastest. The range of valid values depends on the pingroup. See
    "DRVDN_SLWR" in the Tegra TRM.
- nvidia,slew-rate-falling: Integer. Controls falling signal slew rate. 0 is
    fastest. The range of valid values depends on the pingroup. See
    "DRVUP_SLWF" in the Tegra TRM.

Note that many of these properties are only valid for certain specific pins
or groups. See the Tegra TRM and various pinmux spreadsheets for complete
details regarding which groups support which functionality. The Linux pinctrl
driver may also be a useful reference, since it consolidates, disambiguates,
and corrects data from all those sources.

Valid values for pin and group names are:

  mux groups:

    These all support nvidia,function, nvidia,tristate, and many support
    nvidia,pull.

    ata, atb, atc, atd, ate, cdev1, cdev2, crtp, csus, dap1, dap2, dap3, dap4,
    ddc, dta, dtb, dtc, dtd, dte, dtf, gma, gmb, gmc, gmd, gme, gpu, gpu7,
    gpv, hdint, i2cp, irrx, irtx, kbca, kbcb, kbcc, kbcd, kbce, kbcf, lcsn,
    ld0, ld1, ld2, ld3, ld4, ld5, ld6, ld7, ld8, ld9, ld10, ld11, ld12, ld13,
    ld14, ld15, ld16, ld17, ldc, ldi, lhp0, lhp1, lhp2, lhs, lm0, lm1, lpp,
    lpw0, lpw1, lpw2, lsc0, lsc1, lsck, lsda, lsdi, lspi, lvp0, lvp1, lvs,
    owc, pmc, pta, rm, sdb, sdc, sdd, sdio1, slxa, slxc, slxd, slxk, spdi,
    spdo, spia, spib, spic, spid, spie, spif, spig, spih, uaa, uab, uac, uad,
    uca, ucb, uda.

  tristate groups:

    These only support nvidia,pull.

    ck32, ddrc, pmca, pmcb, pmcc, pmcd, pmce, xm2c, xm2d, ls, lc, ld17_0,
    ld19_18, ld21_20, ld23_22.

  drive groups:

    With some exceptions, these support nvidia,high-speed-mode,
    nvidia,schmitt, nvidia,low-power-mode, nvidia,pull-down-strength,
    nvidia,pull-up-strength, nvidia,slew-rate-rising, nvidia,slew-rate-falling.

    drive_ao1, drive_ao2, drive_at1, drive_at2, drive_cdev1, drive_cdev2,
    drive_csus, drive_dap1, drive_dap2, drive_dap3, drive_dap4, drive_dbg,
    drive_lcd1, drive_lcd2, drive_sdmmc2, drive_sdmmc3, drive_spi, drive_uaa,
    drive_uab, drive_uart2, drive_uart3, drive_vi1, drive_vi2, drive_xm2a,
    drive_xm2c, drive_xm2d, drive_xm2clk, drive_sdio1, drive_crt, drive_ddc,
    drive_gma, drive_gmb, drive_gmc, drive_gmd, drive_gme, drive_owr,
    drive_uda.

Example:

	pinctrl@70000000 {
		compatible = "nvidia,tegra20-pinmux";
		reg = < 0x70000014 0x10    /* Tri-state registers */
			0x70000080 0x20    /* Mux registers */
			0x700000a0 0x14    /* Pull-up/down registers */
			0x70000868 0xa8 >; /* Pad control registers */
	};

Example board file extract:

	pinctrl@70000000 {
		sdio4_default: sdio4_default {
			atb {
				nvidia,pins = "atb", "gma", "gme";
				nvidia,function = "sdio4";
				nvidia,pull = <0>;
				nvidia,tristate = <0>;
			};
		};
	};

	sdhci@c8000600 {
		pinctrl-names = "default";
		pinctrl-0 = <&sdio4_default>;
	};