Dell Precision 5820

[janstadt]

Hello. I am trying to extract the bios files from this bios: https://dl.dell.com/FOLDER11491866M/1/M33X_2.36.0.exe . I am following this tutorial: https://github.com/xCuri0/ReBarUEFI/wiki/Enabling-hidden-4G-decoding as i am trying to enable rebar on the machine and it required a bios bin file. After some poking around i found this utility and am able to get bin files (produces 2 folders: 3 CombineBiosName2 v99.1.45 and 2 CombineBiosName2 v99.1.45). Within those folders there are a number of bin files.

I choose 3 CombineBiosName2 v99.1.45 -- 1 System BIOS [V0 AMI] v2.36.0.bin or 2 CombineBiosName2 v99.1.45 -- 1 System BIOS [V0 AMI] v2.36.0.bin and using UEFITool do a search for "4G Decod" and it finds entries and when i select extract body it seems to extract a file, but when i run it against ifrextractor (.\ifrextractor.exe .\4GDecodBody.bin) it doesnt produce anything. This is all over my head but was hoping to get some help. If there is somewhere else i can ask for that'd be great as well.

[NikolajSchlej]

Ref Prompt: "Memory Map IO above 4GB", Help: "This field enables or disables 64bit capable PCI devices to be decoded in above 4GB address space (Only if system supports 64 bit PCI decoding).
This setting will be enabled if Thunderbolt™ Technology Support is enabled.
", QuestionFlags: 0x0, QuestionId: 0x31, VarStoreId: 0x0, VarStoreInfo: 0xFFFF, FormId: 0x8912

[NikolajSchlej]

	Form FormId: 0x8912, Title: "Memory Map IO above 4GB"
		Subtitle Prompt: "Memory Map IO above 4GB", Help: "", Flags: 0x0
		End 
		Subtitle Prompt: "", Help: "", Flags: 0x0
		End 
		GrayOutIf 
			EqIdVal QuestionId: 0xCF3, Value: 0x0
				EqIdVal QuestionId: 0x185, Value: 0x0
				Not 
				Or 
			End 
			CheckBox Prompt: "Memory Map IO above 4GB", Help: "This field enables or disables 64bit capable PCI devices to be decoded in above 4GB address space (Only if system supports 64 bit PCI decoding).
This setting will be enabled if Thunderbolt™ Technology Support is enabled.
", QuestionFlags: 0x10, QuestionId: 0x1A0, VarStoreId: 0x1, VarOffset: 0xFB4, Flags: 0x0, Default: Disabled, MfgDefault: Disabled
				Default DefaultId: 0x0 Value: 1
				Default DefaultId: 0x1 Value: 1
			End 
		End 
		Guid Guid: A5D58BCF-EB5C-44FC-9122-CA4369B9ABE6, Optional data: [29, 224, 206, 122, 65, 169, 111, 130, 74, 153, 215, 249, 177, 221, 39, 30, 72, 31, 14, 0, 0]
	End 

[NikolajSchlej]

VarStore Guid: EC87D643-EBA4-4BB5-A1E5-3F3E36B20DA9, VarStoreId: 0x1, Size: 0x1669, Name: "Setup"

[NikolajSchlej]

Your mistake was searching for "4G Decod" instead of "Above 4G".

[JustCryen]

@janstadt
Sorry for bothering you, I have been trying to do the same with my Dell XPS 13 9380, have you been successful with enabling Resizable BAR on your system?

I have been researching the topic a bit and I have figured out that my bios, even though it's not make this option available for users, likely has Above 4G activated by default (?)

OneOf Prompt: "Memory Remap", Help: "Enable/Disable Memory Remap above 4GB"
			OneOfOption Option: "Enabled" Value: 1, Default, MfgDefault
			OneOfOption Option: "Disabled" Value: 0

But it also seems to have a conditional MMIO option.

OneOf Prompt: "Above 4GB MMIO BIOS assignment", Help: "Enable/Disable above 4GB MemoryMappedIO BIOS assignment
This is enabled automatically when Aperture Size is set to 2048MB."
			OneOfOption Option: "Enabled" Value: 1
			OneOfOption Option: "Disabled" Value: 0, Default, MfgDefault

And the Aperture Size option is also hidden in the bios.

OneOf Prompt: "Aperture Size", Help: "Select the Aperture Size"
			OneOfOption Option: "128MB" Value: 0
			OneOfOption Option: "256MB" Value: 1, Default, MfgDefault
			OneOfOption Option: "512MB" Value: 3
			OneOfOption Option: "1024MB" Value: 7
			OneOfOption Option: "2048MB" Value: 15

I want the ReBAR mostly for my eGPU. For now I figured out that it seems to be enabled on my integrated GPU but not on the external GPU over Thunderbolt.
On eGPU:

On iGPU:

But it seems to be a false reading as the VRAM accessible to the CPU on the iGPU seems to be 0MB

I have also found threads suggesting that ReBAR over Thunderbolt is not always possible / desirable.
https://egpu.io/forums/laptop-computing/resizable-bar-support-for-egpus-possible/

Any idea what to do in this situation?

[Charlyo]

@JustCryen Did you have any success enabling rebar for the rest of GPUs?

[JustCryen]

@Charlyo
It seems like integrated and dedicated graphics have ReBAR already enabled.
I have tried this also on another machine (Intel NUC)
But external graphics running through a Thunderbolt 3 dock does not seem to support ReBAR.

I have no idea if it can be enabled to work with Thunderbolt 3.