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    Subject[PATCH 10/10] ehci-dbgp,documentation: Documentation updates for ehci-dbgp
    Add missing information about requirements of using the EHCI usb debug
    controller as well as to mention you can use a debug controller other
    than the first one in the system.

    Signed-off-by: Jason Wessel <>
    Cc: Greg KH <>
    Cc: Ingo Molnar <>
    Cc: Andrew Morton <>
    Cc: Yinghai Lu <>
    Cc: "Eric W. Biederman" <>
    Cc: Alan Stern <>
    Cc: Sarah Sharp <>
    Cc: Randy Dunlap <>
    Documentation/kernel-parameters.txt | 2 +-
    Documentation/x86/earlyprintk.txt | 39 +++++++++++++++++++++++++++++++++-
    2 files changed, 38 insertions(+), 3 deletions(-)

    diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    index dd1a6d4..e709fc0 100644
    --- a/Documentation/kernel-parameters.txt
    +++ b/Documentation/kernel-parameters.txt
    @@ -670,7 +670,7 @@ and is between 256 and 4096 characters. It is defined in the file
    earlyprintk= [X86,SH,BLACKFIN]
    - earlyprintk=dbgp
    + earlyprintk=dbgp[debugController#]

    Append ",keep" to not disable it when the real console
    takes over.
    diff --git a/Documentation/x86/earlyprintk.txt b/Documentation/x86/earlyprintk.txt
    index 607b1a0..f19802c 100644
    --- a/Documentation/x86/earlyprintk.txt
    +++ b/Documentation/x86/earlyprintk.txt
    @@ -7,7 +7,7 @@ and two USB cables, connected like this:

    [host/target] <-------> [USB debug key] <-------> [client/console]

    -1. There are three specific hardware requirements:
    +1. There are a number of specific hardware requirements:

    a.) Host/target system needs to have USB debug port capability.

    @@ -42,7 +42,35 @@ and two USB cables, connected like this:
    This is a small blue plastic connector with two USB connections,
    it draws power from its USB connections.

    - c.) Thirdly, you need a second client/console system with a regular USB port.
    + c.) You need a second client/console system with a high speed USB 2.0
    + port.
    + d.) The Netchip device must be plugged directly into the physical
    + debug port on the "host/target" system. You cannot use a USB hub in
    + between the physical debug port and the "host/target" system.
    + The EHCI debug controller is bound to a specific physical USB
    + port and the Netchip device will only work as an early printk
    + device in this port. The EHCI host controllers are electrically
    + wired such that the EHCI debug controller is hooked up to the
    + first physical and there is no way to change this via software.
    + You can find the physical port through experimentation by trying
    + each physical port on the system and rebooting. Or you can try
    + and use lsusb or look at the kernel info messages emitted by the
    + usb stack when you plug a usb device into various ports on the
    + "host/target" system.
    + Some hardware vendors do not expose the usb debug port with a
    + physical connector and if you find such a device send a complaint
    + to the hardware vendor, because there is no reason not to wire
    + this port into one of the physically accessible ports.
    + e.) It is also important to note, that many versions of the Netchip
    + device require the "client/console" system to be plugged into the
    + right and side of the device (with the product logo facing up and
    + readable left to right). The reason being is that the 5 volt
    + power supply is taken from only one side of the device and it
    + must be the side that does not get rebooted.

    2. Software requirements:

    @@ -56,6 +84,13 @@ and two USB cables, connected like this:
    (If you are using Grub, append it to the 'kernel' line in

    + On systems with more than one EHCI debug controller you must
    + specify the correct EHCI debug controller number. The ordering
    + comes from the PCI bus enumeration of the EHCI controllers. The
    + default with no number argument is "0" the first EHCI debug
    + controller. To use the second EHCI debug controller, you would
    + use the command line: "earlyprintk=dbgp1"
    NOTE: normally earlyprintk console gets turned off once the
    regular console is alive - use "earlyprintk=dbgp,keep" to keep
    this channel open beyond early bootup. This can be useful for

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      Last update: 2009-07-31 17:11    [W:0.025 / U:5.724 seconds]
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