xref: /kernel/linux/linux-6.6/Documentation/devicetree/bindings/bus/nvidia,tegra20-gmi.txt (revision 62306a36)

Device tree bindings for NVIDIA Tegra Generic Memory Interface bus

The Generic Memory Interface bus enables memory transfers between internal and
external memory. Can be used to attach various high speed devices such as
synchronous/asynchronous NOR, FPGA, UARTS and more.

The actual devices are instantiated from the child nodes of a GMI node.

Required properties:
 - compatible : Should contain one of the following:
        For Tegra20 must contain "nvidia,tegra20-gmi".
        For Tegra30 must contain "nvidia,tegra30-gmi".
 - reg: Should contain GMI controller registers location and length.
 - clocks: Must contain an entry for each entry in clock-names.
 - clock-names: Must include the following entries: "gmi"
 - resets : Must contain an entry for each entry in reset-names.
 - reset-names : Must include the following entries: "gmi"
 - #address-cells: The number of cells used to represent physical base
   addresses in the GMI address space. Should be 2.
 - #size-cells: The number of cells used to represent the size of an address
   range in the GMI address space. Should be 1.
 - ranges: Must be set up to reflect the memory layout with three integer values
   for each chip-select line in use (only one entry is supported, see below
   comments):
   <cs-number> <offset> <physical address of mapping> <size>

Note that the GMI controller does not have any internal chip-select address
decoding, because of that chip-selects either need to be managed via software
or by employing external chip-select decoding logic.

If external chip-select logic is used to support multiple devices it is assumed
that the devices use the same timing and so are probably the same type. It also
assumes that they can fit in the 256MB address range. In this case only one
child device is supported which represents the active chip-select line, see
examples for more insight.

The chip-select number is decoded from the child nodes second address cell of
'ranges' property, if 'ranges' property is not present or empty chip-select will
then be decoded from the first cell of the 'reg' property.

Optional child cs node properties:

 - nvidia,snor-data-width-32bit: Use 32bit data-bus, default is 16bit.
 - nvidia,snor-mux-mode: Enable address/data MUX mode.
 - nvidia,snor-rdy-active-before-data: Assert RDY signal one cycle before data.
   If omitted it will be asserted with data.
 - nvidia,snor-rdy-active-high: RDY signal is active high
 - nvidia,snor-adv-active-high: ADV signal is active high
 - nvidia,snor-oe-active-high: WE/OE signal is active high
 - nvidia,snor-cs-active-high: CS signal is active high

  Note that there is some special handling for the timing values.
  From Tegra TRM:
  Programming 0 means 1 clock cycle: actual cycle = programmed cycle + 1

 - nvidia,snor-muxed-width: Number of cycles MUX address/data asserted on the
   bus. Valid values are 0-15, default is 1
 - nvidia,snor-hold-width: Number of cycles CE stays asserted after the
   de-assertion of WR_N (in case of SLAVE/MASTER Request) or OE_N
   (in case of MASTER Request). Valid values are 0-15, default is 1
 - nvidia,snor-adv-width: Number of cycles during which ADV stays asserted.
   Valid values are 0-15, default is 1.
 - nvidia,snor-ce-width: Number of cycles before CE is asserted.
   Valid values are 0-15, default is 4
 - nvidia,snor-we-width: Number of cycles during which WE stays asserted.
   Valid values are 0-15, default is 1
 - nvidia,snor-oe-width: Number of cycles during which OE stays asserted.
   Valid values are 0-255, default is 1
 - nvidia,snor-wait-width: Number of cycles before READY is asserted.
   Valid values are 0-255, default is 3

Example with two SJA1000 CAN controllers connected to the GMI bus. We wrap the
controllers with a simple-bus node since they are all connected to the same
chip-select (CS4), in this example external address decoding is provided:

gmi@70009000 {
	compatible = "nvidia,tegra20-gmi";
	reg = <0x70009000 0x1000>;
	#address-cells = <2>;
	#size-cells = <1>;
	clocks = <&tegra_car TEGRA20_CLK_NOR>;
	clock-names = "gmi";
	resets = <&tegra_car 42>;
	reset-names = "gmi";
	ranges = <4 0 0xd0000000 0xfffffff>;

	bus@4,0 {
		compatible = "simple-bus";
		#address-cells = <1>;
		#size-cells = <1>;
		ranges = <0 4 0 0x40100>;

		nvidia,snor-mux-mode;
		nvidia,snor-adv-active-high;

		can@0 {
			reg = <0 0x100>;
			...
		};

		can@40000 {
			reg = <0x40000 0x100>;
			...
		};
	};
};

Example with one SJA1000 CAN controller connected to the GMI bus
on CS4:

gmi@70009000 {
	compatible = "nvidia,tegra20-gmi";
	reg = <0x70009000 0x1000>;
	#address-cells = <2>;
	#size-cells = <1>;
	clocks = <&tegra_car TEGRA20_CLK_NOR>;
	clock-names = "gmi";
	resets = <&tegra_car 42>;
	reset-names = "gmi";
	ranges = <4 0 0xd0000000 0xfffffff>;

	can@4,0 {
		reg = <4 0 0x100>;
		nvidia,snor-mux-mode;
		nvidia,snor-adv-active-high;
		...
	};
};