Linux Mailbox framework overview

Revision as of 17:10, 5 October 2021 by Registered User
Applicable for STM32MP15x lines

This article gives information about the Linux® mailbox framework. The mailbox framework is involved in interprocessor communication in heterogeneous multicore systems.

1. Framework purpose[edit source]

The mailbox is used in interprocessor communication to exchange messages or signals between the host and the coprocessor cores. The mailbox framework is based on:

  • A mailbox controller that is platform dependent:
    • It is in charge of configuring and handling IRQ from the IPCC peripheral.
    • It provides a generic API to the mailbox client.
  • A mailbox client that is in charge of the message to send or receive.

A general presentation of the mailbox framework is available in the Linux mailbox documentation [1].

2. System overview[edit source]

Mailbox overview.png

2.1. Component description[edit source]

  • Mailbox controller
The mailbox controller is the stm32_ipcc. It configures and controls the IPCC peripheral
  • Mailbox client
The user can define his own mailbox client.
For example, the RPMsg framework uses mailbox for the interprocessor communication.
In this case the mailbox client is the remoteproc driver that forwards services from/to the RPMsg framework.

2.2. API description[edit source]

The APIs are described in the Linux documentation:

  • Mailbox client API [2]
  • Mailbox controller API [3]

3. Configuration[edit source]

Activate stm32 IPCC mailbox in kernel configuration using the Linux Menuconfig tool: Menuconfig or how to configure kernel

Device drivers  --->
    -*- Mailbox Hardware Support  --->
        <*> STM32 IPCC Mailbox 

4. Device tree configuration[edit source]

The mailbox device node must be declared and enabled in the Linux kernel device tree. Here is an extract of the STM32MP1 evaluation board device tree:

ipcc: mailbox@4c001000 {
	compatible = "st,stm32mp1-ipcc";
	#mbox-cells = <1>;
	reg = <0x4c001000 0x400>;
	st,proc-id = <0>;
	interrupts-extended =
		<&exti 61 1>;
	interrupt-names = "rx", "tx";
	clocks = <&rcc_clk IPCC>;
	power-domains = <&pd_core>;
	status = "disabled";

Then client has to reserve channels. Here is an example of channel allocation for the remoteproc node:

&m4_rproc {
	memory-region = <&retram>, <&mcuram>, <&mcuram2>, <&vdev0vring0>,
			<&vdev0vring1>, <&vdev0buffer>, <&mcu_rsc_table>;
	mboxes = <&ipcc 0>, <&ipcc 1>, <&ipcc 2>;
	mbox-names = "vq0", "vq1", "shutdown";
	interrupt-parent = <&exti>;
	interrupts = <68 1>;
	status = "okay";

5. How to trace and debug the framework[edit source]

5.1. How to trace[edit source]

Dynamic debug traces can be added using the following commands:

echo -n 'file stm32-ipcc.c +p' > /sys/kernel/debug/dynamic_debug/control
echo -n 'file mailbox.c +p' > /sys/kernel/debug/dynamic_debug/control

6. References[edit source]