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Above 4G MMIO support #128

Open miczyg1 opened 2 years ago

miczyg1 commented 2 years ago

The problem you're addressing (if any) Dasharo/edk2 does not support over 4G MMIO on PCI.

Describe the solution you'd like Enable support for 4G MMIO and maybe add an setup option for it.

Where is the value to a user, and who might that user be? Platforms with many PCIe/TBT hotpluggable ports may not fit whole prefetchable memory for them. Some GPUs may also have large memory resources which would need to be allocated above 4G.

Describe alternatives you've considered None

Additional context None

miczyg1 commented 1 year ago

Code complete for fixing 4G MMIO: https://github.com/Dasharo/edk2/pull/26 Not sure if there is a need for a setup option for it. What firmware should do if it can't fit everything below 4G, e.g. because of large dGPU BARs?

zirblazer commented 1 year ago

On propietary Firmwares, above 4 GiB decoding and enabling ReBAR are separate options, albeit enabling ReBAR has as prerequisite the former. With no ReBAR, dGPUs have a sort of standard 256 MiB MMIO window since at least 15 years ago or so, and unless you have a VERY niche setup (Some mining system with PCIe multiplexers and many, many cards), I don't expect it to be realistic to saturate it. Not sure ThunderBolt MMIO requeriments. For reference, I had personally used a setup in 2010 with an AM3 Athlon II X4, the 785G IGP (Radeon 4200) plus two Radeon 5770s using good old 32 Bits Windows XP SP3, and I had like 2.87 GiB RAM visible or so.