From 2475ff9d2c6ea3bbfed55c4635426c371f9ad327 Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Tue, 23 Oct 2012 14:55:08 +0100 Subject: arm64: Add simple earlyprintk support This patch adds support for "earlyprintk=" parameter on the kernel command line. The format is: earlyprintk=[,][,] where is the name of the (UART) device, e.g. "pl011", is the I/O address. The aren't currently used. The mapping of the earlyprintk device is done very early during kernel boot and there are restrictions on which functions it can call. A special early_io_map() function is added which creates the mapping from the pre-defined EARLY_IOBASE to the device I/O address passed via the kernel parameter. The pgd entry corresponding to EARLY_IOBASE is pre-populated in head.S during kernel boot. Only PL011 is currently supported and it is assumed that the interface is already initialised by the boot loader before the kernel is started. Signed-off-by: Catalin Marinas Acked-by: Arnd Bergmann --- Documentation/arm64/memory.txt | 2 ++ 1 file changed, 2 insertions(+) (limited to 'Documentation/arm64') diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt index d758702fc03c..5f583af0a6e1 100644 --- a/Documentation/arm64/memory.txt +++ b/Documentation/arm64/memory.txt @@ -35,6 +35,8 @@ ffffffbc00000000 ffffffbdffffffff 8GB vmemmap ffffffbe00000000 ffffffbffbbfffff ~8GB [guard, future vmmemap] +ffffffbffbc00000 ffffffbffbdfffff 2MB earlyprintk device + ffffffbffbe00000 ffffffbffbe0ffff 64KB PCI I/O space ffffffbbffff0000 ffffffbcffffffff ~2MB [guard] -- cgit v1.2.3-59-g8ed1b