From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Mon, 24 Oct 2016 12:06:29 +0200 Subject: Question about arm64 earlycon In-Reply-To: References: Message-ID: <4966376.bRx4fgSjbT@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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: > > 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