On Fri, 11 May 2012, Sarah Sharp wrote: > On Fri, May 11, 2012 at 03:14:37PM -0400, Alan Stern wrote: > > On Fri, 11 May 2012, Sarah Sharp wrote: > > > > > > That reminds me... I think this should not be so closely linked with > > > > ACPI. There's a perfectly good USB Clear-Feature request for turning > > > > off port power; that's what we should use. If hooks are required for > > > > interfacing with platform-specific code (such as ACPI), they can be > > > > added at the appropriate places. > > > > > > So would you rather userspace issue a clear port power feature request > > > to the roothub through libusb than have a sysfs file per port in > > > /sys/bus/usb/devices/../power/ ? Or are you just saying that the sysfs > > > interface should issue the request to the hub (which may be the > > > roothub), and the xHCI driver can just implement the ACPI calls in its > > > roothub control method? > > > > The latter. Except that the ACPI calls may need to occur in more > > places than just xhci-hcd (ehci-hcd, for example). > > Only the xHCI host controller will have the port power off mechanism. You're only talking about the upcoming Intel implementation, right? > > And what about ports on the USB-2 "rate-matching" hubs that Intel now > > builds into its chipsets? > > For the Intel platform that has the port power off mechanism, there are > EHCI host controllers, but the port switch over changes *all* the USB > ports under xHCI. Leaving aside the matter of people who don't use the port switch-over, what about other platforms? > > For that matter, is it really necessary to involve ACPI in port power > > changes at all? Why can't xhci-hcd simply set the PP bit in the PORTSC > > register, and rely on the PPC bit in the HCCPARAMS register to indicate > > whether or not port power control is supported? In other words, what > > advantage does ACPI have over USB native power control? > > The port power off mechanism is controlled by some other chunk of > hardware outside the xHCI host controller. I asked the architects why > they didn't just use the port power control bits in the port status > registers, but they had already made their design choices by then. So > we're stuck with the ACPI method of powering off the ports. Then yes, xhci_hub_control() would need an ACPI hook. The hook belongs there, not in usbcore. Can you convince the architects to do it the right way next time? :-) Alan Stern -- 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
