diff options
Diffstat (limited to 'Documentation/x86/earlyprintk.txt')
| -rw-r--r-- | Documentation/x86/earlyprintk.txt | 39 |
1 files changed, 37 insertions, 2 deletions
diff --git a/Documentation/x86/earlyprintk.txt b/Documentation/x86/earlyprintk.txt index 607b1a01606..f19802c0f48 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 /etc/grub.conf) + 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 |