[+cc linux-pci] On Tue, Jan 14, 2014 at 11:47 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Tue, 14 Jan 2014, Sarah Sharp wrote: > >> Hi Alan, > > I'm not a good person to ask about this. Maybe Bjorn can help. > >> All this info is second- or third-hand, so please excuse the extremely >> vague bug report. >> >> A new Intel Atom system (Baytrail) comes with both an xHCI host and an >> EHCI host, but the BIOS has an "EHCI only" option that hides the xHCI >> host PCI device from the operating system. It appears that when the >> BIOS is in this mode, the EHCI PCI interrupt is disabled, and the host >> simply doesn't work. >> >> Jamie and Gaggery have more details about the system and the exact >> failure mode. They can provide dmesg as well as a PCI register space >> dump, if necessary. (Jamie and Gaggery, please note, a publicly >> archived mailing list is Cc'ed.) >> >> A customer reports that the following patch fixes the issue: >> >> diff --git a/drivers/usb/host/ehci-pci.c b/drivers/usb/host/ehci-pci.c >> index 3e86bf4371b3..e77566a021ec 100644 >> --- a/drivers/usb/host/ehci-pci.c >> +++ b/drivers/usb/host/ehci-pci.c >> @@ -112,6 +112,9 @@ static int ehci_pci_setup(struct usb_hcd *hcd) >> case PCI_VENDOR_ID_INTEL: >> if (pdev->device == PCI_DEVICE_ID_INTEL_CE4100_USB) >> hcd->has_tt = 1; >> + /* Baytrail BIOS in EHCI only mode fails to enable interrupts */ >> + if (pdev->device == 0x0f34) >> + pci_intx(pdev, 1); >> break; >> case PCI_VENDOR_ID_TDI: >> if (pdev->device == PCI_DEVICE_ID_TDI_EHCI) >> >> I looked through the USB PCI initialization code, and I can't find any >> place where interrupts are enabled, so I assume the PCI core is supposed >> to enable interrupts? Or is it assumed that the system boots with all >> PCI device interrupts enabled? In that case, is it a BIOS issue? > > As I recall, the original PCI spec did not include any way to enable or > disable interrupts -- a rather surprising omission. It was added > later on. > > Anyhow, this is all handled in the PCI core. The device driver > shouldn't need to do much more than pci_enable_device() (which handles > power plus I/O and memory resources) and pci_set_master() (which > handles DMA). Nothing about enabling interrupt generation. > > A quick search did not show any place where the PCI core explicitly > enables interrupts on new devices, so maybe it does assume that the > firmware always enables them. I don't know what guarantees (if any) a > BIOS is supposed to fulfill. > > It seems like the best place to fix this is probably in the PCI core. I think dev->irq is supposed to be valid after pci_enable_device(), so it seems like it would make sense to clear PCI_COMMAND_INTX_DISABLE there. I don't know why a BIOS would leave PCI_COMMAND_INTX_DISABLE set for the EHCI device. Does it support MSI, and the BIOS assumes the OS should use that? I don't see any MSI support in the EHCI code. In any case, this doesn't seem like something we need to depend on the BIOS to do for us. Bjorn -- 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
