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    Subject[PATCH 02/10] xhci: 'noxhci_port_switch' kernel parameter
    Date
    From: Dan Williams <dan.j.williams@intel.com>

    Add a command line switch for disabling ehci port switchover. Useful
    for working around / debugging xhci incompatibilities where ehci
    operation is available.

    Reference: http://marc.info/?l=linux-usb&m=138920063001509&w=2

    Cc: Sarah Sharp <sarah.a.sharp@linux.intel.com>
    Cc: Mathias Nyman <mathias.nyman@linux.intel.com>
    Cc: Holger Hans Peter Freyther <holger@moiji-mobile.com>
    Suggested-by: Alan Stern <stern@rowland.harvard.edu>
    Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
    ---
    Documentation/kernel-parameters.txt | 3 +++
    drivers/usb/host/pci-quirks.c | 15 +++++++++++++--
    2 files changed, 16 insertions(+), 2 deletions(-)

    diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    index 4384217..fc3403114 100644
    --- a/Documentation/kernel-parameters.txt
    +++ b/Documentation/kernel-parameters.txt
    @@ -2251,6 +2251,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.

    nox2apic [X86-64,APIC] Do not enable x2APIC mode.

    + noxhci_port_switch
    + [USB] Use EHCI instead of XHCI where available
    +
    cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
    CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
    Some features depend on CPU0. Known dependencies are:
    diff --git a/drivers/usb/host/pci-quirks.c b/drivers/usb/host/pci-quirks.c
    index 00661d3..38bfe3d 100644
    --- a/drivers/usb/host/pci-quirks.c
    +++ b/drivers/usb/host/pci-quirks.c
    @@ -823,6 +823,15 @@ static int handshake(void __iomem *ptr, u32 mask, u32 done,
    return -ETIMEDOUT;
    }

    +static int noxhci_port_switch;
    +
    +static int __init noxhci_port_switch_setup(char *str)
    +{
    + noxhci_port_switch = 1;
    + return 0;
    +}
    +early_param("noxhci_port_switch", noxhci_port_switch_setup);
    +
    /*
    * Intel's Panther Point chipset has two host controllers (EHCI and xHCI) that
    * share some number of ports. These ports can be switched between either
    @@ -860,8 +869,7 @@ void usb_enable_intel_xhci_ports(struct pci_dev *xhci_pdev)
    return;

    /* Don't switchover the ports if the user hasn't compiled the xHCI
    - * driver. Otherwise they will see "dead" USB ports that don't power
    - * the devices.
    + * driver or has explicitly disabled switchover
    */
    if (!IS_ENABLED(CONFIG_USB_XHCI_HCD)) {
    dev_warn(&xhci_pdev->dev,
    @@ -871,6 +879,9 @@ void usb_enable_intel_xhci_ports(struct pci_dev *xhci_pdev)
    "USB 3.0 devices will work at USB 2.0 speeds.\n");
    usb_disable_xhci_ports(xhci_pdev);
    return;
    + } else if (noxhci_port_switch) {
    + usb_disable_xhci_ports(xhci_pdev);
    + return;
    }

    /* Read USB3PRM, the USB 3.0 Port Routing Mask Register
    --
    1.8.3.2


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