[HOW TO] OpenCore 0.7.4 > 0.7.5 differences

Monthly message by vit9696 , please read it carefully, there is no better place to see what's new in OpenCore.
https://dortania.github.io/hackintosh/updates/2021/11/01/acidanthera-november.html

Main changes applied in 0.7.5 version:

• Improved Linux boot and revised OpenLinuxBoot documentation
• Fixed external drive icons
• Updated builtin firmware versions for SMBIOS
• Updated recovery downloading commands to include Big Sur and Monterey
• Added support for GPU Resize BAR (RBAR).

config.plist

• Booter >> Quirks >> ResizeAppleGpuBars (integer) whose default value is -1 (disables this quirk); reduces GPU PCI BAR size to be compatible with macOS
• UEFI >> Quirks >> ResizeGpuBars (integer) whose default value is -1 (disables this quirk); configure the GPU PCI BAR size for systems other than macOS; leaving it at -1 prevents this value from being applied by OpenCore to Windows or Linux.

Kexts

• AppleALC 1.6.6 (new layouts added)
• BrcmPatchRAM 2.6.1 (Improved BlueToolFixup compatibility with macOS 12) \*
• HibernationFixup 1.4.5 (improved behaviour when battery level is critical)
• Lilu 1.5.7 (improved support for all 64-bit macOS versions)
• VoodooPS2 2.2.7 (fixes)
• VoodooRMI 1.3.5 (fixes, added new devices)
• WhateverGreen 1.5.5 (improved backlight control in AMD RX 5000 series, fixed black screen in Skylake and newer).

\* Monterey has brought major problems for third-party (non-native Apple) wifi and bluetooth devices. Developers are working hard to fix these problems. Little by little improvements are being made but we are still not 100%.

Notes about Resizable BAR (base address register)

Resizable BAR (RBAR) is a technology included in the PCI Express 3.0 specification since 2008 but until now it has been very little used. In AMD it is called Smart Access Memory (SAM). Its purpose is to increase the amount of VRAM (graphics card memory) that is accessible by the CPU. The limit has been kept at 256MB of VRAM memory for backward compatibility.

What RBAR does is allow the CPU to access all of the VRAM memory. The only restriction is imposed by the GPU itself. In theory the CPU can access all the VRAM but in practice the GPU always has the priority of use.
Its main advantage is in graphically demanding games. In this type of game, the CPU collaborates with the GPU performing the necessary calculation tasks for the execution of the game. Without RBAR, the CPU can only load 256MB into VRAM and the rest has to be loaded into RAM, which slows down the GPU from reading the data. With RBAR, all or most of the computational tasks performed by the CPU are stored in the VRAM, making them available to the GPU with less wait times.

In order to use RBAR, certain requirements must be met:

• compatible graphics card (currently in Hackintosh only AMD 6000 series)
• motherboard with this option in BIOS
• compatible CPU (Intel 9-10-11 generations and AMD Zen 3 series).

Note: really almost any GPU supports resize bar but most likely they do not benefit from the performance improvement.

OpenCore 0.7.4 has added support for RBAR by adding 2 quirks:

• Booter >> Quirks >> ResizeAppleGpuBars: reduces GPU PCI BAR size to be compatible with macOS.
• UEFI >> Quirks >> ResizeGpuBars: configure the GPU PCI BAR size for systems other than macOS.

ResizeAppleGpuBars affects only to macOS and ResizeGpuBars affects all other operating systems.

Note from vit9696: ResizeAppleGpuBars should be 0 for boards supporting resize bar and -1 for boards that do not. 9 and 10 will cause sleep wake crashes on macOS with most GPUs and 8 will cause excessive memory usage on some GPUs without any useful benefit.