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  • Catalin Marinas's avatar
    arm64: Add simple earlyprintk support · 2475ff9d
    Catalin Marinas authored
    
    
    This patch adds support for "earlyprintk=" parameter on the kernel
    command line. The format is:
    
      earlyprintk=<name>[,<addr>][,<options>]
    
    where <name> is the name of the (UART) device, e.g. "pl011", <addr> is
    the I/O address. The <options> 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: default avatarCatalin Marinas <catalin.marinas@arm.com>
    Acked-by: default avatarArnd Bergmann <arnd@arndb.de>
    2475ff9d