Question about arm64 earlycon

Arnd Bergmann
2016-10-24T10:06:29Z

On Sunday, October 23, 2016 12:26:59 AM CEST Duc Dang wrote:
> Hi Catalin, Marc, Mark, Arnd,
>
> I am testing with 3.12 kernel with earlyprintk enabled and I see some
> garbage characters in the console log right before the message
> indicating that the real console device is initialized:
>
> <some garbage characters here>01c020000.serial: ttyS0 at MMIO
> 0x1c020000 (irq = 108, base_baud = 3125000) is a U6_16550A
> console [ttyS0] enabled, bootconsole disabled
>
> I looked through early_prink.c file and printk.c file and it looks
> like there is case that some early boot code can touch the UART
> hardware via ealy console driver while the 'real' console driver is
> setting up the same UART port? Please let me know if I missed some
> important piece of code that can prevent this.

I don't think we every supported earlyprintk on arm64, and
earlycon support may have been added later.

If you can't use a modern kernel, try backporting all the
relevant earlycon changes.

Arnd