Cannot Get Tpm To Work - Un-allowed Dma Capable Bus

Hey all. I have a Dell Inspiron 3668 desktop with a fresh OEM install of Windows 10 Home x64. It has no external peripherals with the exception of a mini pci-e WiFi card and a SATA slim DVD ROM. I want to enable drive encryption, and I know I can't use BitLocker because it's the Home version of Windows, but I should still be able to use the generic Microsoft drive encryption feature under Settings >> Update and Security. Problem is, it isn't there. When I check my TPM (2.0) in tpm.msc it says it's ready for use, but when I go to System Information (run as admin) I get the message "reasons for failed automatic device encryption: un-allowed DMA capable bus". I know there's some white/blacklisting for the DMA bus, so I went to the device manager and got the hardware ID of my TPM and compared it against the "unallowed" items in the registry (under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\DmaSecurity\Default), but didn't see it there. I even created a key for the TPM and added it to the "Allowed" folder, still nothing. It's enabled as PTT in the UEFI. Can anybody help me to figure out why it's un-allowed? Thanks.

 

Thanks for the reply. I tried what you suggested, but it didn't change anything unfortunately. I'd actually also done a clear previously within tpm.msc without success. I the UEFI I have the TPM enabled under PTT. If I disable it the message in System info changes to "TPM not usable...something something". I think what I need to do is determine which bus is un-allowed, but I'm not sure how I would do that...