Optiplex 990, BIOS A23, Compatibility issues

Hello. We are an OEM designer for add-on hardware and a supplier to Dell (15+ years to date). Respectively facing a quirk with the Dell Optiplex 990 chassis where our add-on adapter is unable to install on Windows 10 Pro 64 bit (with current updates). We have invested 12+ hours into this review and can share the following details:

1) Dell Bios was A06 -> upgraded first to A10 -> now upto A23 (latest as of this writing).

2) We have a transparent PCIe to PCI bridge onboard from Pericom which was showing random yellow bangs in Device Manager. After some research, the power configuration of Windows -> turning OFF the Rapid Power up boot feature fixed this quirk. Thanks to the public poster for this juicy piece of information.

3) After resolving the above, the PCI to PCI bridge is now enabled correctly as shown in Device Manager. Next issue is our PCI function controller which is not being granted resources and is yellow marked. We have full compatibility with Windows 10 32 and 64 bit with signed device drivers. No other client is facing the same issues on this target OS.

4) To rule out Windows, we have booted with FreeDOS and ran our utility which dumps the values of our PCI function -> reads the BAR0 value -> performs an ERASE of our firmware (Microwire EEprom) -> writes and then verifies the write of the firmware. This FreeDOS tool which we use for production also failed. Noted that the BAR0 value is 0000 which is incorrect.

Q: Is there a BIOS configuration that we may have missed to allow enabling of such add-on PCI to PCI bridges?

Q: We understand that some PC vendors do not support the full IDSEL line ranges for the secondary side of the PCI bridges. Could this be an issue? As the adapter under test and PC is not local to us, we have not yet tested to move the IDSEL onto different address lines to work around this quirk.

Summary: It appears that this motherboard, with all updates, is not properly supporting this popular PCIe to PCI bridge. Conclusion is based on the lack of granting resources to the secondary side PCI functions - BAR0 = 0000.

We deem this case to be serious so will continue the investigation by sourcing this box and/or motherboard for a detailed review. The temp work around is to shift to a native PCIe design, which we have. Welcome all feedback. Many thanks for reading this post. 

Latest BIOS was sourced here.