2009/6/25 Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>: > >> Before the console is set up, the printk data is formatted >> and put into the kernel log buffer, but not sent to any console. >> Any messages printk'ed before that are buffered but do not >> appear. When the console is initialized, then all buffered >> messages are sent to the console, and subsequent printks cause >> the message to go to the log buffer, but then immediately >> get sent from there to the console. >> >> Under certain conditions you can examine the log buffer of >> a kernel that failed to initialize it's console, after a >> warm reset of the machine, using the firmware memory dump >> command. > > On ppc, we have tricks to display things earlier :-) > > We can initialize the serial ports way before console_setup() (and we do > in most cases) and we use what we call the "udbg" console until the real > one takes over. The "udbg" console is a very small layer which outputs > via a provided "putc" routine. Platforms can provide their own here, we > have a collection of standard ones for legacy UARTs (it should be > automatically setup in that case by the code in legacy_serial), Apple > ESCCs, etc... We even have compile time options that allow that stuff to > be initialized before start_kernel... Thank you. This is what I described and want to understand. The arch/powerpc/kernel/legacy_serial.c do find_legacy_serial_ports then take a default serial port by using open firmware device tree information. The find_legacy_serial_ports() called form setup_arch but I don't know who call setup_arch (setup_32.c)function. Can you give me a hint ? Thanks in advanced. BRs, H. Johnny -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
