Commit a28ab162 authored by Krzysztof Kozlowski's avatar Krzysztof Kozlowski Committed by Jonathan Corbet

Documentation: ARM: EXYNOS: Describe boot loaders interface

Various boot loaders for Exynos based boards use certain memory
addresses during booting for different purposes. Mostly this is one of
following :
1. as a CPU boot address,
2. for storing magic cookie related to low power mode (AFTR, sleep).

The document, based solely on kernel source code, tries to group the
information scattered over different files. This would help in the
future when adding support for new SoC or when extending features
related to low power modes.
Signed-off-by: default avatarKrzysztof Kozlowski <k.kozlowski.k@gmail.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent b322582f
Interface between kernel and boot loaders on Exynos boards
==========================================================
Author: Krzysztof Kozlowski
Date : 6 June 2015
The document tries to describe currently used interface between Linux kernel
and boot loaders on Samsung Exynos based boards. This is not a definition
of interface but rather a description of existing state, a reference
for information purpose only.
In the document "boot loader" means any of following: U-boot, proprietary
SBOOT or any other firmware for ARMv7 and ARMv8 initializing the board before
executing kernel.
1. Non-Secure mode
Address: sysram_ns_base_addr
Offset Value Purpose
=============================================================================
0x08 exynos_cpu_resume_ns System suspend
0x0c 0x00000bad (Magic cookie) System suspend
0x1c exynos4_secondary_startup Secondary CPU boot
0x1c + 4*cpu exynos4_secondary_startup (Exynos4412) Secondary CPU boot
0x20 0xfcba0d10 (Magic cookie) AFTR
0x24 exynos_cpu_resume_ns AFTR
0x28 + 4*cpu 0x8 (Magic cookie, Exynos3250) AFTR
2. Secure mode
Address: sysram_base_addr
Offset Value Purpose
=============================================================================
0x00 exynos4_secondary_startup Secondary CPU boot
0x04 exynos4_secondary_startup (Exynos542x) Secondary CPU boot
4*cpu exynos4_secondary_startup (Exynos4412) Secondary CPU boot
0x20 exynos_cpu_resume (Exynos4210 r1.0) AFTR
0x24 0xfcba0d10 (Magic cookie, Exynos4210 r1.0) AFTR
Address: pmu_base_addr
Offset Value Purpose
=============================================================================
0x0800 exynos_cpu_resume AFTR
0x0814 exynos4_secondary_startup (Exynos4210 r1.1) Secondary CPU boot
0x0818 0xfcba0d10 (Magic cookie, Exynos4210 r1.1) AFTR
0x081C exynos_cpu_resume (Exynos4210 r1.1) AFTR
3. Other (regardless of secure/non-secure mode)
Address: pmu_base_addr
Offset Value Purpose
=============================================================================
0x0908 Non-zero (only Exynos3250) Secondary CPU boot up indicator
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