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ed8444006d
Mark the first 128 MiB of DRAM as reserved. The first 128 MiB of DRAM
may optionally be used by TFA and other firmware for its own purposes,
and in such case, Linux must not use this memory.
On this platform, U-Boot runs in EL3 and starts TFA BL31 and Linux from
a single combined fitImage. U-Boot has full access to all memory in the
0x40000000..0xbfffffff range, as well memory in the memory banks in the
64-bit address ranges, and therefore U-Boot patches this full complete
view of platform memory layout into the DT that is passed to the next
stage.
The next stage is TFA BL31 and then the Linux kernel. The TFA BL31 does
not modify the DT passed from U-Boot to TFA BL31 and then to Linux with
any new reserved-memory {} node to reserve memory areas used by the TFA
BL31 to prevent the next stage from using those areas, which lets Linux
to use all of the available DRAM as described in the DT that was passed
in by U-Boot, including the areas that are newly utilized by TFA BL31.
In case of high DRAM utilization, for example in case of four instances
of "memtester 3900M" running in parallel, unless the memory used by TFA
BL31 is properly reserved, Linux may use and corrupt the memory used by
TFA BL31, which would often lead to system becoming unresponsive.
Until TFA BL31 can properly fill its own reserved-memory node into the
DT, and to assure older versions of TFA BL31 do not cause problems, add
explicitly reserved-memory {} node which prevents Linux from using the
first 128 MiB of DRAM.
Note that TFA BL31 can be adjusted to use different memory areas, this
newly added reserved-memory {} node follows longer-term practice on the
R-Car SoCs where the first 128 MiB of DRAM is reserved for firmware use.
In case user does modify TFA BL31 to use different memory ranges, they
must either use a future version of TFA BL31 which properly patches a
reserved-memory {} node into the DT, or they must adjust the address
ranges of this reserved-memory {} node accordingly.
Fixes:
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Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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Start your kernel development journey here: * Getting Started: Documentation/process/development-process.rst * Your First Patch: Documentation/process/submitting-patches.rst * Coding Style: Documentation/process/coding-style.rst * Build System: Documentation/kbuild/index.rst * Development Tools: Documentation/dev-tools/index.rst * Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst * Core APIs: Documentation/core-api/index.rst Academic Researcher ------------------- Explore the kernel's architecture and internals: * Researcher Guidelines: Documentation/process/researcher-guidelines.rst * Memory Management: Documentation/mm/index.rst * Scheduler: Documentation/scheduler/index.rst * Networking Stack: Documentation/networking/index.rst * Filesystems: Documentation/filesystems/index.rst * RCU (Read-Copy Update): Documentation/RCU/index.rst * Locking Primitives: Documentation/locking/index.rst * Power Management: Documentation/power/index.rst Security Expert --------------- Security documentation and hardening guides: * Security Documentation: Documentation/security/index.rst * LSM Development: Documentation/security/lsm-development.rst * Self Protection: Documentation/security/self-protection.rst * Reporting Vulnerabilities: Documentation/process/security-bugs.rst * CVE Procedures: Documentation/process/cve.rst * Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst * Security Features: Documentation/userspace-api/seccomp_filter.rst Backport/Maintenance Engineer ----------------------------- Maintain and stabilize kernel versions: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * Backporting Guide: Documentation/process/backporting.rst * Applying Patches: Documentation/process/applying-patches.rst * Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git for Maintainers: Documentation/maintainer/configure-git.rst System Administrator -------------------- Configure, tune, and troubleshoot Linux systems: * Admin Guide: Documentation/admin-guide/index.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst * Tracing/Debugging: Documentation/trace/index.rst * Performance Security: Documentation/admin-guide/perf-security.rst * Hardware Monitoring: Documentation/hwmon/index.rst Maintainer ---------- Lead kernel subsystems and manage contributions: * Maintainer Handbook: Documentation/maintainer/index.rst * Pull Requests: Documentation/maintainer/pull-requests.rst * Managing Patches: Documentation/maintainer/modifying-patches.rst * Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst * Development Process: Documentation/process/maintainer-handbooks.rst * Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst * Git Configuration: Documentation/maintainer/configure-git.rst Hardware Vendor --------------- Write drivers and support new hardware: * Driver API Guide: Documentation/driver-api/index.rst * Driver Model: Documentation/driver-api/driver-model/driver.rst * Device Drivers: Documentation/driver-api/infrastructure.rst * Bus Types: Documentation/driver-api/driver-model/bus.rst * Device Tree Bindings: Documentation/devicetree/bindings/ * Power Management: Documentation/driver-api/pm/index.rst * DMA API: Documentation/core-api/dma-api.rst Distribution Maintainer ----------------------- Package and distribute the kernel: * Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst * ABI Documentation: Documentation/ABI/README * Kernel Configuration: Documentation/kbuild/kconfig.rst * Module Signing: Documentation/admin-guide/module-signing.rst * Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst * Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst AI Coding Assistant ------------------- CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and follow the AI coding assistants documentation before contributing to the Linux kernel: * Documentation/process/coding-assistants.rst This documentation contains essential requirements about licensing, attribution, and the Developer Certificate of Origin that all AI tools must comply with. 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