GOP:Frame Buffer memory type?

[Evan Lloyd <Evan.Lloyd@arm.com>]

The EFI_GRAPHICS_OUTPUT_PROTOCOL provides for a frame buffer:
"FrameBufferBase  Base  address of graphics linear frame buffer. Info contains information required to allow software to draw directly to the frame buffer without using Blt().Offset zero in FrameBufferBase represents the upper left pixel of the display."

The spec is silent on how (or if) the frame buffer should appear in the memory map.  The obvious option is EfiMemoryMappedIO, however the spec has (Table 29. "Memory Type Usage after ExitBootServices") :
"EfiMemoryMappedIO
This memory is not used by the OS. All system memory-mapped IO information should come from ACPI tables."
This is slightly problematic because the GOP Frame Buffer is not described in an ACPI table.

Most options are obviously unusable (like "EfiBootServicesData  Memory available for general use.") as the "available for general use" basically means overwritten by OS memory usage, so the pixels corrupt OS data.

So -  can anyone advise us on whether there is some "Standard" way of doing this, is this an undefined area, or have we missed something?

Regards,
Evan

Evan Lloyd | Technical Lead for Windows on Arm | Arm
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