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No Boot when graphics card in lower PCIe slot

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jwdevel View Drop Down
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    Posted: 31 Jul 2019 at 11:10pm
My system:

* Mobo: ASRock X570 Phantom Gaming 4
* CPU: AMD Ryzen 7 2700X
* 32G ECC memory
* GPU: see below
* Currently running Debian Linux

My goal is to use two graphics cards: (1) NVidia GeForce GTX 1660 Ti and (2) Radeon RX 580
(eventual goal is GPU passthrough/IOMMU virtualization)

However, whenever there is any graphics card in the bottom x16 PCIe slot (PCIE3), the machine does not boot.

Note: it *does* get to the BIOS setup screen. However, after that the screen goes blank, and makes no progress. I do not see the GRUB boot loader screen, for instance.

In this hung state, there *is* a video signal (my monitor would show a "no signal" message otherwise), but it is blank. Also, the motherboard light is off, so it has passed all of those health checks.
Lastly, in this hung state, the network light for the LAN is off (in case that is helpful).

Here are things I've tried:

1. Nvidia card in the PCIE1 slot, alone - boots OK
2. Radeon card in the PCIE1 slot, alone - boots OK
3. Nvidia card in the PCIE3 slot, alone - no boot
4. Nvidia card in the PCIE3 slot, alone - no boot
5. Nvidia card in the PCIE1 slot, Radeon in the PCIE3 slot - no boot (this is what I eventually want to work).

I have updated to the newest available BIOS version (P1.30). No change.
I have reset CMOS. No change.

The manual indicates that PCIE3 should support a graphics card in x4 mode.
But even with a single card in this slot, I cannot make it work.

Anyone have advice on this?

I contacted ASRock support, and gave them the above information, and I got a 1-line reply back: "Motherboard support no more than 2 video cards".

So, either they misunderstood me, or they meant to write "no more than 1 video card".

But from the documentation I find, and even the printed manual, the second x16 PCIe slot should support a graphics card.
And even with a single card in the system, in that second slot, it does not boot.

So, the tech support does not seem... very helpful (:

Anyone here have ideas?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jwdevel Quote  Post ReplyReply Direct Link To This Post Posted: 01 Aug 2019 at 10:18am
I resolved this issue, thanks to some help elsewhere. For posterity, the magic setting was to disable CSM in the BIOS.

In my BIOS, the setting is named: "Boot\CSM Compatibility" (set to Disabled).

Then, I had to re-install my OS because the old one was installed under CSM mode (not using UEFI).

But the CSM disable was the step that made it able to recognize the video card in the second x16 slot.

I haven't gotten the VM w/passthrough set up yet, but past this hurdle at least.
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