On AARCH64, there is no requirement to support OSes that can only access ACPI tables in low memory (i.e., below 4 GB), and there are reasons to prefer allocations higher up. First of all, since DMA capable devices may only be able to access 32-bit addressable memory, we may prefer to reserve low memory for DMA buffers. Additionally, keeping memory reservations close together makes it easier for the OS to map system RAM efficiently (with as few levels of translation as possible)
So introduce a PCD that specifies which ACPI versions should be supported, and omit 32-bit only tables and allocations below 4 GB if the PCD indicates that we only target ACPI 2.0 or higher (#1). Set the PCD for ArmVirtQemu (#2) Changes since v4: - don't change the handling of the FACS table, it is loaded in low memory for other reasons than the address size of the ACPI table entries, and does not exist on arm64 anyway. - drop BdsDxe patch for now, more discussion is needed - implement review feedback from Star Ard Biesheuvel (2): MdeModulePkg: AcpiTableDxe: make 4 GB table allocation limit optional ArmVirtPkg/ArmVirtQemu: limit ACPI support to v5.0 and higher ArmVirtPkg/ArmVirtQemu.dsc | 4 + MdeModulePkg/MdeModulePkg.dec | 11 + MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiSdt.c | 3 +- MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableDxe.inf | 3 + MdeModulePkg/Universal/Acpi/AcpiTableDxe/AcpiTableProtocol.c | 441 ++++++++++++-------- 5 files changed, 278 insertions(+), 184 deletions(-) -- 2.5.0 _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel
