I have a BD795m motherboard running BIOS version 1.02.
When Secure Boot is ON, my RTX 5090 consistently trains at full PCIe Gen4 x16 (16GT/s).
When Secure Boot is OFF, the PCIe link always falls back to Gen1 (2.5GT/s).
This happens even on warm reboots, with correct GPU seating, NVMe slot, CMOS cleared, and after cleaning MOK.
Any suggestions?
@matthewpowers Hey, thanks! And yeah, I’ve actually seen something pretty close to what you’re describing on a few boards. The weird part is that Secure Boot can absolutely change how the board trains PCIe lanes, so what you’re seeing isn’t unheard of. Also, I haven't checked is 1.0.2 the latest version of the BIOS available for the BD board? You have probably checked but I would just make sure you are running the latest and greatest. Again, something you have probably already checked.
A couple things I’d check because they usually cause the Gen1 fallback...and also just a note, I don't have my BD795M board available to me as I am typing out this reply back, so can't check to see if these are settings that are available in the BIOS of my board, but check to see if these are there:
PCIe power saving / ASPM - On some boards, if ASPM or PCIe power optimization is enabled, the GPU will drop to 2.5 GT/s unless Secure Boot is on. Try disabling ASPM or any PCIe power saving options in the BIOS.
Above 4G Decoding and Resizable BAR - VAST seems to like these being on from what I remember. Make sure both are enabled. Sometimes toggling both off, rebooting, and then turning them back on forces the PCIe link to retrain the slot correctly.
CSM When Secure Boot is off, some of these boards turn CSM back on. CSM can cuase GPUs to link at Gen 1. Make sure CSM is disabled for sure and that you are booting pure UEFI.
Let me know if these are settings you have played around with? Thanks Matt!
Brandon