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7389fa945f
With >= 4GB memory installed we get a memory map split in the middle due to remap that has boundaries that are inconveniently aligned for MTRRs due to the various UMA regions. 0000MB-2780MB 2780MB RAM (writeback) 2780MB-2782MB 2MB TSEG (uncached/SMRR) 2782MB-2784MB 2MB GFX GTT (uncached) 2784MB-2816MB 32MB GFX UMA (uncached) 2816MB-4096MB 1280MB EMPTY (N/A) 4096MB-5368MB 1272MB RAM (writeback) 5368MB-5376MB 8MB ME UMA (uncached) The default MTRR allocation method of trying to cover everything with one MTRR and then carve out a single uncached region does not work for the GPU aperture which needs write-combining type, and it also has issues trying to cover the uneven boundaries in the avaiable variable MTRRs. My goal was to make a minimal set of changes and avoid modifying behavior on existing systems with an algorithm that is not always optimal for a typical memory layout. So the flag 'above4gb=2' will change these allocation behaviors: 1) Detect the number of available variable MTRRs rather than limiting to hardcoded value. We need every last MTRR. 2) Don't try to cover all RAM with one MTRR, instead let each RAM region get covered independently. 3) Don't assume uma_memory_base is part of the last region and increase the size of that region. In this case the UMA region is carved out from the lower memory region and it is already declared as part of the ram region. 4) If a memory region can't be covered with MTRRs >= 16MB then instead make a larger region and trim it with uncached MTRRs. Change-Id: I5a60a44ab6d3ae2f46ea6ffa9e3677aaad2485eb Signed-off-by: Duncan Laurie <dlaurie@google.com> Reviewed-on: http://review.coreboot.org/761 Tested-by: build bot (Jenkins) Reviewed-by: Ronald G. Minnich <rminnich@gmail.com> |
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| README | ||
------------------------------------------------------------------------------- coreboot README ------------------------------------------------------------------------------- coreboot is a Free Software project aimed at replacing the proprietary BIOS (firmware) found in most computers. coreboot performs a little bit of hardware initialization and then executes additional boot logic, called a payload. With the separation of hardware initialization and later boot logic, coreboot can scale from specialized applications that run directly firmware, run operating systems in flash, load custom bootloaders, or implement firmware standards, like PC BIOS services or UEFI. This allows for systems to only include the features necessary in the target application, reducing the amount of code and flash space required. coreboot was formerly known as LinuxBIOS. Payloads -------- After the basic initialization of the hardware has been performed, any desired "payload" can be started by coreboot. See http://www.coreboot.org/Payloads for a list of supported payloads. Supported Hardware ------------------ coreboot supports a wide range of chipsets, devices, and mainboards. For details please consult: * http://www.coreboot.org/Supported_Motherboards * http://www.coreboot.org/Supported_Chipsets_and_Devices Build Requirements ------------------ * gcc / g++ * make Optional: * doxygen (for generating/viewing documentation) * iasl (for targets with ACPI support) * gdb (for better debugging facilities on some targets) * ncurses (for 'make menuconfig') * flex and bison (for regenerating parsers) Building coreboot ----------------- Please consult http://www.coreboot.org/Build_HOWTO for details. Testing coreboot Without Modifying Your Hardware ------------------------------------------------ If you want to test coreboot without any risks before you really decide to use it on your hardware, you can use the QEMU system emulator to run coreboot virtually in QEMU. Please see http://www.coreboot.org/QEMU for details. Website and Mailing List ------------------------ Further details on the project, a FAQ, many HOWTOs, news, development guidelines and more can be found on the coreboot website: http://www.coreboot.org You can contact us directly on the coreboot mailing list: http://www.coreboot.org/Mailinglist Copyright and License --------------------- The copyright on coreboot is owned by quite a large number of individual developers and companies. Please check the individual source files for details. coreboot is licensed under the terms of the GNU General Public License (GPL). Some files are licensed under the "GPL (version 2, or any later version)", and some files are licensed under the "GPL, version 2". For some parts, which were derived from other projects, other (GPL-compatible) licenses may apply. Please check the individual source files for details. This makes the resulting coreboot images licensed under the GPL, version 2.