On Sat, 15 Dec 2018, Marc MERLIN wrote: > Hi Greg, > > On Sat, Dec 15, 2018 at 08:59:45AM +0100, Greg KH wrote: > > > How do I know whether a PCI USB card I'm buying is a "discrete USB > > > controller" as per how it's used in that sentence? > > > > If the PCI card has a USB host controller on it. I think almost anyone > > you buy will be like that. > > Ok, that's what I thought. Basically I need multiple USB host > controllers since each of them will have a limit of 32. Motheroards have > one or two? Usually they do. Not always. > If I see: > 00:14.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB xHCI (rev 05) > 00:1a.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB EHCI #2 (rev 05) > 00:1d.0 USB controller: Intel Corporation 8 Series/C220 Series Chipset Family USB EHCI #1 (rev 05) > > Does it mean that I should indeed have 2 separate USB controllers for > USB-2 if I know where to tap and therefore should have a 64 device limit > if I spread the load? EHCI is not subject to the 32-device limit of xHCI. A single EHCI controller can handle up to 126 devices. But of course, EHCI only supports high speed (480 Mb/s), not SuperSpeed (>= 5000 Mb/s). On the other hand, many computers are wired with all the external USB ports connected to one of the controllers on the motherboard. The other controller may be connected to a few internal devices or to nothing at all. > > > Or does it just say that basically you're doubling your limit with > > > another card, which is what I already did, and then you hit the limit > > > again? > > > > Probably, there is a limit on how many devices a USB host controller can > > handle at once, that's just the way the hardware works. > > Keep adding PCI cards :) > > Right, but my 1U servers only allow a single PCI card. Is there even > such a thing as a PCI(e) card that has multiple USB host controllers? > Clearly the one I bought only has a single. > > 05:00.0 USB controller: Fresco Logic FL1100 USB 3.0 Host Controller (rev 10) Yes, there are such cards. But whether you can find one with multiple USB-3 controllers is a different question. Alan Stern
