| Message ID | Pine.LNX.4.44L0.1807021302210.1574-100000@iolanthe.rowland.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Dear Alan, Thank you very much for looking into this issue. Am 02.07.2018 um 19:19 schrieb Alan Stern: > On Mon, 2 Jul 2018, Alan Stern wrote: > >>>>> The problem is, that currently 100 ms sleep is over 10 % of the overall >>>>> execution time of the Linux kernel here. So I really like to not sleep >>>>> if it’s not needed. >>>> >>>> It would be nice to execute the probes in parallel; that would reduce >>>> the total delay to 50 ms. However, that is the subject of a separate >>>> discussion. >>>> >>>>>> Besides, doesn't it seem like a bad idea to reset the controller while >>>>>> leaving devices on the USB bus in whatever state they happened to be? >>>>> >>>>> Yes, it’s probably not optimal. >>>>> >>>>> I wonder if the reset is needed, if the firmware has already initialized >>>>> the device. >>>> >>>> The devices on the bus need to be reset, because the OS has no idea of >>>> what they are and what the firmware has them doing. >>>> >>>> For example, the firmware may have assigned bus address 2 to a >>>> keyboard. But the OS can initialize the devices in a different order, >>>> and it might want to assign bus address 2 to a USB drive. Then you'd >>>> have two devices trying to use the same address at the same time, which >>>> would not be a good thing. >>> >>> Understood. >>> >>> So, what would be a way forward? Add a whitelist for boards or chipsets >>> not needing the 50 ms delay? >> >> The 50-ms delay isn't for the board or the chipset; it is for the USB >> devices that are plugged into the controller. It is required by the >> USB spec, so we can't get rid of it. > > I may have been too hasty. The drivers for other types of USB host > controllers do not perform a USB bus reset during startup, so maybe > OHCI doesn't really need it either. > > We still need to put the controller into the correct state, but what > happens to the bus shouldn't matter. This is because reinitializing > the controller disables all its ports, and the only way to enable a > port is by sending a reset signal through it. So the attached devices > will end up getting reset one way or another, even if we don't do it > explicitly during the handoff. > > Therefore in theory we should be okay without the 50-ms delay at all. > And we might as well tell the controller to go into the USB_RESET even > if it already is in that state; testing the current state is more > effort than just doing setting it. Something like the patch below > ought to work, although I wouldn't submit it for the -stable kernels > since it doesn't fix a real bug. > > It's not clear why OHCI has both a USB_RESET state and a > HostControllerReset command, especially since the command changes the > state to USB_SUSPEND instead of USB_RESET. This is just one of several > odd things in the OHCI specification. > Index: usb-4.x/drivers/usb/host/pci-quirks.c > =================================================================== > --- usb-4.x.orig/drivers/usb/host/pci-quirks.c > +++ usb-4.x/drivers/usb/host/pci-quirks.c > @@ -783,15 +783,9 @@ static void quirk_usb_handoff_ohci(struc > /* disable interrupts */ > writel((u32) ~0, base + OHCI_INTRDISABLE); > > - /* Reset the USB bus, if the controller isn't already in RESET */ > - if (control & OHCI_HCFS) { > - /* Go into RESET, preserving RWC (and possibly IR) */ > - writel(control & OHCI_CTRL_MASK, base + OHCI_CONTROL); > - readl(base + OHCI_CONTROL); > - > - /* drive bus reset for at least 50 ms (7.1.7.5) */ > - msleep(50); > - } > + /* Go into the USB_RESET state, preserving RWC (and possibly IR) */ > + writel(control & OHCI_CTRL_MASK, base + OHCI_CONTROL); > + readl(base + OHCI_CONTROL); > > /* software reset of the controller, preserving HcFmInterval */ > if (!no_fminterval) Tested on ASRock E350M1 with GRUB as bootloader, and a mouse attached to the USB port. The mouse works under X. Kind regards, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Index: usb-4.x/drivers/usb/host/pci-quirks.c =================================================================== --- usb-4.x.orig/drivers/usb/host/pci-quirks.c +++ usb-4.x/drivers/usb/host/pci-quirks.c @@ -783,15 +783,9 @@ static void quirk_usb_handoff_ohci(struc /* disable interrupts */ writel((u32) ~0, base + OHCI_INTRDISABLE); - /* Reset the USB bus, if the controller isn't already in RESET */ - if (control & OHCI_HCFS) { - /* Go into RESET, preserving RWC (and possibly IR) */ - writel(control & OHCI_CTRL_MASK, base + OHCI_CONTROL); - readl(base + OHCI_CONTROL); - - /* drive bus reset for at least 50 ms (7.1.7.5) */ - msleep(50); - } + /* Go into the USB_RESET state, preserving RWC (and possibly IR) */ + writel(control & OHCI_CTRL_MASK, base + OHCI_CONTROL); + readl(base + OHCI_CONTROL); /* software reset of the controller, preserving HcFmInterval */ if (!no_fminterval)