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After reviewing OvmfPkg's use of its own QemuFwCfgLib instances, it is clear that its only pre-DXE fw_cfg dependency concerns S3 support (the QemuFwCfgS3Enabled() call in "PlatformPei/Platform.c"). For ARM guests, S3 is in the distant future, but we can see several shorter term applications for fw_cfg that all reside in DXE: - controlling boot order (to be implemented in PlatformBdsLib for Intel BDS), - supporting -kernel / -initrd / -append boot on QEMU (to be implemented in PlatformBdsLib for Intel BDS, similarly), - loading and linking ACPI tables, - installing SMBIOS tables. Therefore it makes sense to add a simple MMIO-based fw_cfg client library to ArmVirtualizationPkg that for the moment is only available to DXE_DRIVER modules. Because MMIO accesses are costly on KVM/ARM, InternalQemuFwCfgReadBytes() accesses the fw_cfg data register in full words. This speeds up transfers almost linearly. Contributed-under: TianoCore Contribution Agreement 1.0 Signed-off-by: Laszlo Ersek <lersek@redhat.com> git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16567 6f19259b-4bc3-4df7-8a09-765794883524