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OMAP2+ and K3 Mailbox
The OMAP mailbox hardware facilitates communication between different processors
using a queued mailbox interrupt mechanism. The IP block is external to the
various processor subsystems and is connected on an interconnect bus. The
communication is achieved through a set of registers for message storage and
interrupt configuration registers.
Each mailbox IP block/cluster has a certain number of h/w fifo queues and output
interrupt lines. An output interrupt line is routed to an interrupt controller
within a processor subsystem, and there can be more than one line going to a
specific processor's interrupt controller. The interrupt line connections are
fixed for an instance and are dictated by the IP integration into the SoC
(excluding the SoCs that have a Interrupt Crossbar IP). Each interrupt line is
programmable through a set of interrupt configuration registers, and have a rx
and tx interrupt source per h/w fifo. Communication between different processors
is achieved through the appropriate programming of the rx and tx interrupt
sources on the appropriate interrupt lines.
The number of h/w fifo queues and interrupt lines dictate the usable registers.
All the current OMAP SoCs except for the newest DRA7xx SoC has a single IP
instance. DRA7xx has multiple instances with different number of h/w fifo queues
and interrupt lines between different instances. The interrupt lines can also be
routed to different processor sub-systems on DRA7xx as they are routed through
the Crossbar, a kind of interrupt router/multiplexer. The K3 AM65x and J721E
SoCs has each of these instances form a cluster and combine multiple clusters
into a single IP block present within the Main NavSS. The interrupt lines from
all these clusters are multiplexed and routed to different processor subsystems
over a limited number of common interrupt output lines of an Interrupt Router.
Mailbox Device Node:
A Mailbox device node is used to represent a Mailbox IP instance/cluster within
a SoC. The sub-mailboxes are represented as child nodes of this parent node.
Required properties:
- compatible: Should be one of the following,
"ti,omap2-mailbox" for OMAP2420, OMAP2430 SoCs
"ti,omap3-mailbox" for OMAP3430, OMAP3630 SoCs
"ti,omap4-mailbox" for OMAP44xx, OMAP54xx, AM33xx,
AM43xx and DRA7xx SoCs
"ti,am654-mailbox" for K3 AM65x and J721E SoCs
- reg: Contains the mailbox register address range (base
address and length)
- interrupts: Contains the interrupt information for the mailbox
device. The format is dependent on which interrupt
controller the Mailbox device uses
- #mbox-cells: Common mailbox binding property to identify the number
of cells required for the mailbox specifier. Should be
- ti,mbox-num-users: Number of targets (processor devices) that the mailbox
device can interrupt
- ti,mbox-num-fifos: Number of h/w fifo queues within the mailbox IP block
SoC-specific Required properties:
The following are mandatory properties for the OMAP architecture based SoCs
- ti,hwmods: Name of the hwmod associated with the mailbox. This
should be defined in the mailbox node only if the node
is not defined as a child node of a corresponding sysc
interconnect node.
The following are mandatory properties for the K3 AM65x and J721E SoCs only:
- interrupt-parent: Should contain a phandle to the TI-SCI interrupt
controller node that is used to dynamically program
the interrupt routes between the IP and the main GIC
controllers. See the following binding for additional
Child Nodes:
A child node is used for representing the actual sub-mailbox device that is
used for the communication between the host processor and a remote processor.
Each child node should have a unique node name across all the different
mailbox device nodes.
Required properties:
- ti,mbox-tx: sub-mailbox descriptor property defining a Tx fifo
- ti,mbox-rx: sub-mailbox descriptor property defining a Rx fifo
Sub-mailbox Descriptor Data
Each of the above ti,mbox-tx and ti,mbox-rx properties should have 3 cells of
data that represent the following:
Cell #1 (fifo_id) - mailbox fifo id used either for transmitting
(ti,mbox-tx) or for receiving (ti,mbox-rx)
Cell #2 (irq_id) - irq identifier index number to use from the parent's
interrupts data. Should be 0 for most of the cases, a
positive index value is seen only on mailboxes that have
multiple interrupt lines connected to the MPU processor.
Cell #3 (usr_id) - mailbox user id for identifying the interrupt line
associated with generating a tx/rx fifo interrupt.
Optional Properties:
- ti,mbox-send-noirq: Quirk flag to allow the client user of this sub-mailbox
to send messages without triggering a Tx ready interrupt,
and to control the Tx ticker. Should be used only on
sub-mailboxes used to communicate with WkupM3 remote
processor on AM33xx/AM43xx SoCs.
Mailbox Users:
A device needing to communicate with a target processor device should specify
them using the common mailbox binding properties, "mboxes" and the optional
"mbox-names" (please see Documentation/devicetree/bindings/mailbox/mailbox.txt
for details). Each value of the mboxes property should contain a phandle to the
mailbox controller device node and an args specifier that will be the phandle to
the intended sub-mailbox child node to be used for communication. The equivalent
"mbox-names" property value can be used to give a name to the communication channel
to be used by the client user.
1. /* OMAP4 */
mailbox: mailbox@4a0f4000 {
compatible = "ti,omap4-mailbox";
reg = <0x4a0f4000 0x200>;
interrupts = <GIC_SPI 26 IRQ_TYPE_LEVEL_HIGH>;
ti,hwmods = "mailbox";
#mbox-cells = <1>;
ti,mbox-num-users = <3>;
ti,mbox-num-fifos = <8>;
mbox_ipu: mbox_ipu {
ti,mbox-tx = <0 0 0>;
ti,mbox-rx = <1 0 0>;
mbox_dsp: mbox_dsp {
ti,mbox-tx = <3 0 0>;
ti,mbox-rx = <2 0 0>;
dsp {
mboxes = <&mailbox &mbox_dsp>;
2. /* AM33xx */
mailbox: mailbox@480c8000 {
compatible = "ti,omap4-mailbox";
reg = <0x480C8000 0x200>;
interrupts = <77>;
ti,hwmods = "mailbox";
#mbox-cells = <1>;
ti,mbox-num-users = <4>;
ti,mbox-num-fifos = <8>;
mbox_wkupm3: wkup_m3 {
ti,mbox-tx = <0 0 0>;
ti,mbox-rx = <0 0 3>;
3. /* AM65x */
&cbass_main {
cbass_main_navss: interconnect0 {
mailbox0_cluster0: mailbox@31f80000 {
compatible = "ti,am654-mailbox";
reg = <0x00 0x31f80000 0x00 0x200>;
#mbox-cells = <1>;
ti,mbox-num-users = <4>;
ti,mbox-num-fifos = <16>;
interrupt-parent = <&intr_main_navss>;
interrupts = <164 0>;
mbox_mcu_r5fss0_core0: mbox-mcu-r5fss0-core0 {
ti,mbox-tx = <1 0 0>;
ti,mbox-rx = <0 0 0>;