Just to add another data point: I’m on an 11th gen mainboard on bios 3.10 with an Intel ARC A770 GPU.
I applied the patch mentioned by @Lee_Holbrook (by running setup_var_cv SaSetup 0x431 1 0x01 ) and successfully activated ReBAR support on Manjaro Unstable with Linux 6.2.6. This gave a noticeable fps improvement and finally make Blender on a 4k monitor responsive.
lspci -vvv reports:
Capabilities: [420 v1] Physical Resizable BAR
BAR 2: current size: 16GB, supported: 256MB 512MB 1GB 2GB 4GB 8GB 16GB
I have been running it like this 5 days without any new instability. This method also seems to survive reboots.
BAR 0 means available space when ReBAR is on … and BAR 2 when ReBAR is off
So when ReBAR is not enabled, the CPU only gets access to a limited VRAM portion of the GPU.
Okay interesting, the tool’s BLOB release files work, but when building from source it can’t open the file… sigh
Now, why is this not available in the BIOS settings? Given how far back for older boards some vendors are making this available this makes me very sad.
Also, coreboot?
I have exactly the same experience with my ARC A750 eGPU and an 11th Gen Framework… I jumped through the hoops to get that tool running (did nobody mention that you’ve got to get a UEFI Shell up somehow, too - and learn to use it (hint: it’s like DOS - FS0: is the USB stick, cd to the path, run it like a program, etc)? haha). Admittedly I didn’t get a “Before”, but in the After, it’s got a half-opinion - says it’s disabled in BIOS, but enabled in the specs.
Maybe it’s just confused by Thunderbolt?
BTW, the ARC A750 worked wonderfully (Satisfactory in DX12 at least locked at 60fps - the ARC is full of quirks and in DX11 it was struggling at 20fps, and Vulkan was a corrupt garbage fire) even before ReBAR tweak was applied.
Can anyone who has an AMD mainboard check if there happens to be a ReBAR option in the BIOS? I doubt that they changed it this time but I’m hoping so. It’s really frustrating that they refuse to add a control for it even though it’s already implemented under the hood.
As a Linux user who successfully utilized an 11th gen + rx590 eGPU setup in the past, I would love to see if this 7840U would run well with an ARC A580 or RX6700XT these days. Thank you for posting this data.
Check what address range AMD preallocates to the TypeC PCIe ports. With Intel, this range is by far not big enough to fit any GPU’s full VRAM. That’d need to be solved first. Only then is it a question of whether the BIOS would support ReBar itself (which it actually might, according to some reports here and it detecting ReBar for some eGPUs in some applications, even though it is not working). Unknown if there are deep limitations of the TB/USB4 controllers.
Here the example of DevMgr, view resources by connection:
Only ~450 MiB per port. Such limits have been pretty standard. My desktop Maple Ridge controller uses ~740 MiB (but that is dual port). Still a far cry from 8 or more GiB.
(Note there will be 2 ranges. One is smaller and for IO, the larger one is the one for the actual VRAM)