On Thu, Jan 12, 2012 at 02:29:47PM -0800, Sarah Sharp wrote: > > > The problem is that since the BMC actually attaches to the host > > > controller, it can impact system power management if all the emulated > > > devices aren't suspended. A couple of Intel server vendors have gotten > > > really cranky about the power management on systems with the EHCI rate > > > matching hub and a BMC. Apparently power management is much worse for > > > unsuspended HIDs under EHCI than under UHCI, since the EHCI periodic > > > frame list keeps getting polled by the EHCI hardware, making the CPU > > > come out of C states, etc. Async endpoints don't cause as big a power > > > draw, but it would benefit system power management overall if they were > > > able to be suspended. > > > > Yes, it would be nice, so please tell those hardware companies to > > implement this in their USB cdrom devices :) > > A couple smart vendors have realized they'll save power if they make the > BMC disconnect the emulated USB devices when the remote admin isn't > connected to the system. I think that's what IBM used to do with their systems a long time ago in order to resolve this issue. > Some of them are even waking up to the fact that they need to have > their devices handle selective suspend. But if the BMC vendor does > support selective suspend for their emulated USB CD drive, and they > don't disconnect when it's not in use, we really need to add support > autosuspend to the Linux sr driver. Hey, patches are always gladly welcome :) > > Otherwise, this sounds like the same problem we had years ago with UHCI > > and USB printers, right? > > That's probably before I joined the linux-usb mailing list, so I don't > know that story. Basically, you plugged in a USB printer, it took down your PCI bus by saturating it with "empty" USB messages. Happened back in the mid-to-late 1990's. There was some major reworks of the UHCI hardware in order to resolve this issue. Geesh, kids these days, not knowing their history :) thanks, greg "get off my lawn" k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
