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Firmware can use EfiMemoryMappedIO to request that MMIO regions be mapped
by the OS so they can be accessed by EFI runtime services, but should have
no other significance to the OS (UEFI r2.10, sec 7.2). However, most
bootloaders and EFI stubs convert EfiMemoryMappedIO regions to
E820_TYPE_RESERVED entries, which prevent Linux from allocating space from
them (see remove_e820_regions()).
Some platforms use EfiMemoryMappedIO entries for PCI MMCONFIG space and PCI
host bridge windows, which means Linux can't allocate BAR space for
hot-added devices.
Remove large EfiMemoryMappedIO regions from the E820 map to avoid this
problem.
Leave small (< 256KB) EfiMemoryMappedIO regions alone because on some
platforms, these describe non-window space that's included in host bridge
_CRS. If we assign that space to PCI devices, they don't work. On the
Lenovo X1 Carbon, this leads to suspend/resume failures.
The previous solution to the problem of allocating BARs in these regions
was to add pci_crs_quirks[] entries to disable E820 checking for these
machines (see
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| .. | ||
| efi_32.c | ||
| efi_64.c | ||
| efi_stub_32.S | ||
| efi_stub_64.S | ||
| efi_thunk_64.S | ||
| efi.c | ||
| Makefile | ||
| quirks.c | ||