#
# Copyright (C) 2013, Miao Yan <miao.yan@windriver.com>
# Copyright (C) 2015, Bin Meng <bmeng.cn@gmail.com>
#
# SPDX-License-Identifier:      GPL-2.0+
#

VxWorks Support
===============

This document describes the information about U-Boot loading VxWorks kernel.

Status
------
U-Boot supports loading VxWorks kernels via 'bootvx' and 'bootm' commands.
For booting old kernels (6.9.x) on PowerPC and ARM, and all kernel versions
on other architectures, 'bootvx' shall be used. For booting VxWorks 7 kernels
on PowerPC and ARM, 'bootm' shall be used.

64-bit x86 kernel cannot be loaded as of today.

VxWork 7 on PowerPC and ARM
---------------------------
From VxWorks 7, VxWorks starts adopting device tree as its hardware decription
mechansim (for PowerPC and ARM), thus requiring boot interface changes.
This section will describe the new interface.

For PowerPC, the calling convention of the new VxWorks entry point conforms to
the ePAPR standard, which is shown below (see ePAPR for more details):

    void (*kernel_entry)(fdt_addr, 0, 0, EPAPR_MAGIC, boot_IMA, 0, 0)

For ARM, the calling convention is show below:

    void (*kernel_entry)(void *fdt_addr)

When booting new VxWorks kernel (uImage format), the parameters passed to bootm
is like below:

    bootm <kernel image address> - <device tree address>

VxWorks bootline
----------------
When using 'bootvx', the kernel bootline must be prepared by U-Boot at a
board-specific address before loading VxWorks. U-Boot supplies its address
via "bootaddr" environment variable. To check where the bootline should be
for a specific board, go to the VxWorks BSP for that board, and look for a
parameter called BOOT_LINE_ADRS. Assign its value to "bootaddr". A typical
value for "bootaddr" is 0x101200.

If a "bootargs" variable is defined, its content will be copied to the memory
location pointed by "bootaddr" as the kernel bootline. If "bootargs" is not
there, command 'bootvx' can construct a valid bootline using the following
environments variables: bootdev, bootfile, ipaddr, netmask, serverip,
gatewayip, hostname, othbootargs.

When using 'bootm', just define "bootargs" in the environment and U-Boot will
handle bootline fix up for the kernel dtb automatically.

Serial console
--------------
It's very common that VxWorks BSPs configure a different baud rate for the
serial console from what is being used by U-Boot. For example, VxWorks tends
to use 9600 as the default baud rate on all x86 BSPs while U-Boot uses 115200.
Please configure both U-Boot and VxWorks to use the same baud rate, or it may
look like VxWorks hangs somewhere as nothing outputs on the serial console.

x86-specific information
------------------------
Before loading an x86 kernel, two additional environment variables need to be
provided. They are "e820data" and "e820info", which represent the address of
E820 table and E820 information (defined by VxWorks) in system memory.

Check VxWorks kernel configuration to look for BIOS_E820_DATA_START and
BIOS_E820_INFO_START, and assign their values to "e820data" and "e820info"
accordingly. If neither of these two are supplied, U-Boot assumes a default
location at 0x4000 for "e820data" and 0x4a00 for "e820info". Typical values
for "e820data" and "e820info" are 0x104000 and 0x104a00. But there is one
exception on Intel Galileo, where "e820data" and "e820info" should be left
unset, which assume the default location for VxWorks.

Note since currently U-Boot does not support ACPI yet, VxWorks kernel must
be configured to use MP table and virtual wire interrupt mode. This requires
INCLUDE_MPTABLE_BOOT_OP and INCLUDE_VIRTUAL_WIRE_MODE to be included in a
VxWorks kernel configuration.