Above 4G MMIO Resource Allocation

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   Hello -

I am trying to use an ASRock J3355M motherboard connected to multiple GPUs. When I connect 3 or more GPUs, the system does not boot (no video output, can't see BIOS messages etc).

With two GPUs or one it boots fine.

I suspect what is happening is that the BIOS is probably trying to allocate the PCIe BAR address ranges below the 4G limit (and with more than two cards, runs out of address space). I note that when I use 2 or fewer GPUs and the system does boot, I can see via lspci that all of the BAR windows are located below 4G.

I went looking around for an option in the BIOS configuration called "Above 4GB MMIO BIOS Assignment" that is present on other ASRock boards (including the J3455 Pro BTC+, which is very similar) but does not seem to be present on the J3355M.

Is there some way to expose this or permit PCIe devices to get allocated above 4G? Is there a test BIOS or something that could enable this option?

Many thanks.

Ben

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bgelb0 Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 18 Jan 2021 Location: USA Status: Offline Points: 3	Post Options Post Reply Quote bgelb0 Report Post Thanks(0) Quote Reply Topic: Above 4G MMIO Resource Allocation Posted: 18 Jan 2021 at 12:49pm
	Hello - I am trying to use an ASRock J3355M motherboard connected to multiple GPUs. When I connect 3 or more GPUs, the system does not boot (no video output, can't see BIOS messages etc). With two GPUs or one it boots fine. I suspect what is happening is that the BIOS is probably trying to allocate the PCIe BAR address ranges below the 4G limit (and with more than two cards, runs out of address space). I note that when I use 2 or fewer GPUs and the system does boot, I can see via lspci that all of the BAR windows are located below 4G. I went looking around for an option in the BIOS configuration called "Above 4GB MMIO BIOS Assignment" that is present on other ASRock boards (including the J3455 Pro BTC+, which is very similar) but does not seem to be present on the J3355M. Is there some way to expose this or permit PCIe devices to get allocated above 4G? Is there a test BIOS or something that could enable this option? Many thanks. Ben