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The code to compute n, m1, m2, p1 divisors is not correct in coreboot and on some targets hits a working mode at lower refresh rate, which is why display is working on some targets. The divisors must be such "refclk * (5 * (m1 + 2) + (m2 + 2))/ (n + 2) / (p1 * p2)" is as close as possible to the target frequency (which is defined by the resolution and refresh rate). This patch also fixes the reference frequency. This patch reuses linux (4.1) code from drivers/gpu/drm/i915/intel_display.c to correctly compute divisors. The result is that some previously not working displays, like many displays found on the Lenovo T60 might work now. Some examples of T60 displays that were known to not work (in payload): Samsung LTN141XA-L01 (14.1" 1024x768) LG-Philips LP150X09 (15.1" 1024x768) IDtech N150U3-L01 (15.1" 1600x1200) IDtech IAQX10N (15.1" 2048x1536) Samsung LTN154X3-L0A (15.4" 1280x800) LG-Philips LP150E06-A5K4 (15.1" 1400x1050) Tested on T60 with 1024x786. Change-Id: I2c7f3bb0024ac005029eaebe3ecdc70c38ac777e Signed-off-by: Arthur Heymans <arthur@aheymans.xyz> Reviewed-on: https://review.coreboot.org/16504 Tested-by: build bot (Jenkins) Reviewed-by: Martin Roth <martinroth@google.com>
------------------------------------------------------------------------------- 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 ------------------ * make * gcc / g++ Because Linux distribution compilers tend to use lots of patches. coreboot does lots of "unusual" things in its build system, some of which break due to those patches, sometimes by gcc aborting, sometimes - and that's worse - by generating broken object code. Two options: use our toolchain (eg. make crosstools-i386) or enable the ANY_TOOLCHAIN Kconfig option if you're feeling lucky (no support in this case). * iasl (for targets with ACPI support) Optional: * doxygen (for generating/viewing documentation) * gdb (for better debugging facilities on some targets) * ncurses (for 'make menuconfig' and 'make nconfig') * 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.