XPS 8940, Resizable BAR not enabling

Question

I'm having an issue enabling Resizable BAR on my XPS 8940. I'm using the latest BIOS (v2.10.0) and have enabled the appropriate setting in the BIOS (yes, I've quadruple-checked this) but unfortunately it is still not enabled in Windows. Both GPU-Z and the Nvidia Control Panel report that it is not, and GPU-Z even lists that it is not enabled in the BIOS:

Anyone have any idea why it might not be enabled?

I should also note that I have a second NVME SSD in the 4x PCIe slot through an adapter which I know was causing issues with Resizable BAR in the past using older BIOS versions, but this doesn't seem to make a difference. I completely removed it but Resizable BAR is still not enabled.

If anyone has any ideas why it is not working, would really appreciate the help.

My config is: i7-11700k, 2x8GB RAM, RTX 3070, 1TB NVME SSD (+secondary thru PCIe), 2TB HDD

rene.kuhs · Answer

Just a quick update, the secondary NVME through the x4 PCIe is no longer present. I changed the SATA Operation from RAID to AHCI with the hopes that that might fix the Resizable BAR issue. Although I successfully changed it with my current Windows install, it doesn't want to boot with that secondary NVME present so I'll have to figure out a different solution for that since changing back from AHCI to RAID is apparently a massive pain in the rear.

Anyway, after all that, Resizable BAR is still not working.

RoHe · Answer

If you didn't reconfigure Windows to use AHCI, before changing that BIOS setting, can you not just reset BIOS back to RAID?

Image the boot drive first to be safe, and you can try this:

Open Cmd prompt window from desktop, run as administrator
Copy-paste this command, which will start Windows in Safe Mode the next time you reboot: bcdedit /set {current} safeboot minimal and press Enter
Restart the computer and enter BIOS setup
Change the SATA Operation mode from AHCI to RAID
Save the change and exit Setup. Windows will automatically boot in Safe Mode
Open Cmd again, as in step #1
Copy-paste this command, which will start Windows in Normal Mode the next time you reboot: bcdedit /deletevalue {current} safeboot and press Enter
Reboot and -hopefully- Windows will automatically start, with BIOS set to RAID

Still may not fix your Resizable BAR issue...

rene.kuhs · Answer

I'm not too concerned with that secondary NVME drive. Changing it back to RAID certainly won't fix the Resizable BAR issue since it wasn't working even when it was set to RAID before, with or without the secondary drive.

I don't currently have an easy way to image my boot drive so I'd prefer not to go through the process of reverting. FYI, the process you outlined is indeed how I changed from RAID to AHCI in the first place.

rene.kuhs · Answer

Thanks for the reply. Unfortunately the link you provided is just in relation to updating the firmware on the GPU which GPU-Z is already reporting to support Resizable BAR. I even checked the vBIOS on the 3070 and it is indeed the latest one from Dell.

The problem seems to be related to the BIOS of the actual motherboard but I can't for the life of me figure it out.

Can anyone confirm that Resizable BAR does actually currently work on an XPS 8940 machine (and I mean confirming through GPU-Z, not just confirming that the checkbox is ticked in the BIOS)

RoHe · Answer

IIRC, you can revert back to RAID that same... You can use Macrium Reflect (free) to image the boot drive and save that image on an external USB HDD.

See if there's anything useful here to fix this...

RoHe · Answer

But at the least, it was a start to make sure your GPU has the firmware to support Resizable BAR.

Support was added for RB in XPS 8940 BIOS v2.2.0. Whether it still works in any/all subsequent BIOS versions is an open question.

I don't have XPS 8940, so I can't answer the question.

RoHe · Answer

That spammer's post has been deleted...

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XPS 8940, Resizable BAR not enabling

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