How are PLX (or other …ASMedia?) PCIe bridges / switches assigned to IOMMU groups?

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1

Hi!

I wonder why i cant find any PCIe T-junction adapters, to phrase it in plumbers nomenclature. AFAIK, there exist PCIe bridges and switches, capable of posing as a cough T-junction (lack of a better term) [bridge?] to the host system, while providing a multiple of the host-supplied amount of lanes on its other end, to be utilised by multiple PCIe devices. I’m imagining a PCIe to dual (or multiple) mini-PCIe adaptor card, which could be very useful to run multiple wireless LAN cards off of the same PCIe slot.

…sticking to the WLAN example, one could run one mPCIe card for each band, in case one doesn’t have an adaptor that’s capable of simultaneous dual-banding …or one wants to run WLAN and a 3G/4G WAN card …or any other imaginable configuration …but has a limited amount of host slots / lanes. …it doesn’t even need to be mPCIe, there’re extension cables, riser cards, etc. …one could macgyver a funny, but properly working, “spider” of PCIe devices… …wow, how about nesting? That’d be very fancy! …LOL, i’m not even trolling, there’re enough examples of sub-standard configurations, sold as “Enterprise Grade” appliances - just look at Peter Brockie’s teardowns on Youtube :wink: :+1:

  1. Am i missing something - why does it not exist, yet?
  2. I’m sure such an adaptor, and all it’s children (connected devices), would be grouped into the same IOMMU group …right?
  3. My personal use case for such an adaptor would be to run multiple WLAN NICs, for simultaneous wireless network supply on both bands, 2G4 and 5GHz …in my router VM.
  4. Not even those creative Chinese (on AliExpress) seem to have come up with such an adaptor. Other sources?
  5. I know, my personal use case resembles a somewhat weak, maybe weird, argument, since i could just use a dedicated AP, or even some USB adapters.
  6. I might be too young for the non-express variant of “PCI”, but haven’t basically almost all of the same pins, of each slot, been connected together …as in bus topology …cough T-junctions cough :wink: …i know there’re PCIe-to-PCI bridges …that might be an option too …any thoughts?
2

The ASRock ITX boards allow you to use a specific electrical riser card to do x8 and x8 from a x16 slot. I’ve yet to see anyone actually attempt that, but it’s worth throwing out there.

3

Oh cool! (I really like ASRock, for many reasons)
So ASRock does the bifurcation on-board, in firmware. Not exactly what i’m looking for, but good to know.

Does ASRock provide / sell those …let’s call 'em “splitter-risers”? Has anyone seen those, yes? What key words would i put into my favourite image search engine to find examples?

4

I literally have no clue who sells those. You may be better off directly inquiring Asrock or talking to @wendell

You should also check out my friend tesla500 on YouTube if you like teardowns. He’s a fan of EEVblog, which also does teardowns.

5

http://www.ameri-rack.com/ARC2-PELY423-C7_m.html
A company that makes those

Shop where i found a price

6

It seems, i didn’t choose my keywords properly. I’ve just found a hot candidate, using “pcie splitter” as ebay search terms: that one :point_right: https://www.ebay.com/itm/253238238652 …it’s not mini-PCIe, but it promises to do what i’m looking for.

7

Actually I am sleepy and didn’t read carefully. Sorry my suggestions were based on @FurryJackman s comment.

8

Nope, that’s not it. The item description states “Please verify with us or your board manufacturer to make sure the board supports bifurcation.” So it’s the (main)board, that needs to support bifurcation. I’m looking for a USB-hub type “splitter” …urgh, no, “splitter” is such a cumbersome word describe what i’m actually looking for - it’s not just board, traces and sockets. I’m looking for something with active logic ICs, like a (well known?) PLX, or a Pericom PI7C9X …see also my other post in this thread (i think i’ve found something)

9

this seems to be crypto coin mining equipment …of course, seems to make sense to create / use alternatives, rather than buying another mobo+cpu+psu+ram …when you run out of PCIe lanes …fascinating!