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NXP i.MX System Controller Firmware (SCFW)
The System Controller Firmware (SCFW) is a low-level system function
which runs on a dedicated Cortex-M core to provide power, clock, and
resource management. It exists on some i.MX8 processors. e.g. i.MX8QM
(QM, QP), and i.MX8QX (QXP, DX).
The AP communicates with the SC using a multi-ported MU module found
in the LSIO subsystem. The current definition of this MU module provides
5 remote AP connections to the SC to support up to 5 execution environments
(TZ, HV, standard Linux, etc.). The SC side of this MU module interfaces
with the LSIO DSC IP bus. The SC firmware will communicate with this MU
using the MSI bus.
System Controller Device Node:
The scu node with the following properties shall be under the /firmware/ node.
Required properties:
- compatible: should be "fsl,imx-scu".
- mbox-names: should include "tx0", "tx1", "tx2", "tx3",
"rx0", "rx1", "rx2", "rx3".
- mboxes: List of phandle of 4 MU channels for tx and 4 MU channels
for rx. All 8 MU channels must be in the same MU instance.
Cross instances are not allowed. The MU instance can only
be one of LSIO MU0~M4 for imx8qxp and imx8qm. Users need
to make sure use the one which is not conflict with other
execution environments. e.g. ATF.
Channel 0 must be "tx0" or "rx0".
Channel 1 must be "tx1" or "rx1".
Channel 2 must be "tx2" or "rx2".
Channel 3 must be "tx3" or "rx3".
mboxes = <&lsio_mu1 0 0
&lsio_mu1 0 1
&lsio_mu1 0 2
&lsio_mu1 0 3
&lsio_mu1 1 0
&lsio_mu1 1 1
&lsio_mu1 1 2
&lsio_mu1 1 3>;
See Documentation/devicetree/bindings/mailbox/fsl,mu.txt
for detailed mailbox binding.
i.MX SCU Client Device Node:
Client nodes are maintained as children of the relevant IMX-SCU device node.
Power domain bindings based on SCU Message Protocol
This binding for the SCU power domain providers uses the generic power
domain binding[2].
Required properties:
- compatible: Should be "fsl,imx8qxp-scu-pd".
- #power-domain-cells: Must be 1. Contains the Resource ID used by
SCU commands.
See detailed Resource ID list from:
Clock bindings based on SCU Message Protocol
This binding uses the common clock binding[1].
Required properties:
- compatible: Should be "fsl,imx8qxp-clock".
- #clock-cells: Should be 1. Contains the Clock ID value.
- clocks: List of clock specifiers, must contain an entry for
each required entry in clock-names
- clock-names: Should include entries "xtal_32KHz", "xtal_24MHz"
The clock consumer should specify the desired clock by having the clock
ID in its "clocks" phandle cell.
See the full list of clock IDs from:
Pinctrl bindings based on SCU Message Protocol
This binding uses the i.MX common pinctrl binding[3].
Required properties:
- compatible: Should be one of:
Required properties for Pinctrl sub nodes:
- fsl,pins: Each entry consists of 3 integers which represents
the mux and config setting for one pin. The first 2
integers <pin_id mux_mode> are specified using a
PIN_FUNC_ID macro, which can be found in
The last integer CONFIG is the pad setting value like
pull-up on this pin.
Please refer to i.MX8QXP Reference Manual for detailed
CONFIG settings.
[1] Documentation/devicetree/bindings/clock/clock-bindings.txt
[2] Documentation/devicetree/bindings/power/power_domain.txt
[3] Documentation/devicetree/bindings/pinctrl/fsl,imx-pinctrl.txt
RTC bindings based on SCU Message Protocol
Required properties:
- compatible: should be "fsl,imx8qxp-sc-rtc";
Example (imx8qxp):
lsio_mu1: mailbox@5d1c0000 {
#mbox-cells = <2>;
firmware {
scu {
compatible = "fsl,imx-scu";
mbox-names = "tx0", "tx1", "tx2", "tx3",
"rx0", "rx1", "rx2", "rx3";
mboxes = <&lsio_mu1 0 0
&lsio_mu1 0 1
&lsio_mu1 0 2
&lsio_mu1 0 3
&lsio_mu1 1 0
&lsio_mu1 1 1
&lsio_mu1 1 2
&lsio_mu1 1 3>;
clk: clk {
compatible = "fsl,imx8qxp-clk";
#clock-cells = <1>;
iomuxc {
compatible = "fsl,imx8qxp-iomuxc";
pinctrl_lpuart0: lpuart0grp {
fsl,pins = <
SC_P_UART0_RX_ADMA_UART0_RX 0x06000020
SC_P_UART0_TX_ADMA_UART0_TX 0x06000020
pd: imx8qx-pd {
compatible = "fsl,imx8qxp-scu-pd";
#power-domain-cells = <1>;
rtc: rtc {
compatible = "fsl,imx8qxp-sc-rtc";
serial@5a060000 {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_lpuart0>;
clocks = <&clk IMX8QXP_UART0_CLK>,
clock-names = "per", "ipg";
power-domains = <&pd IMX_SC_R_UART_0>;