• Kumar Gala's avatar
    [POWERPC] 85xx: Add support for relocatable kernel (and booting at non-zero) · 37dd2bad
    Kumar Gala authored
    Added support to allow an 85xx kernel to be run from a non-zero physical
    address (useful for cooperative asymmetric multiprocessing situations and
    kdump).  The support can be configured at compile time by setting
    CONFIG_PAGE_OFFSET, CONFIG_KERNEL_START, and CONFIG_PHYSICAL_START as
    desired.
    
    Alternatively, the kernel build can set CONFIG_RELOCATABLE.  Setting this
    config option causes the kernel to determine at runtime the physical
    addresses of CONFIG_PAGE_OFFSET and CONFIG_KERNEL_START.  If
    CONFIG_RELOCATABLE is set, then CONFIG_PHYSICAL_START has no meaning.
    However, CONFIG_PHYSICAL_START will always be used to set the LOAD program
    header physical address field in the resulting ELF image.
    
    Currently we are limited to running at a physical address that is a
    multiple of 256M.  This is due to how we map TLBs to cover
    lowmem.  This should be fixed to allow 64M or maybe even 16M alignment
    in the future.  It is considered an error to try and run a kernel at a
    non-aligned physical address.
    
    All the magic for this support is accomplished by proper initialization
    of the kernel memory subsystem and use of ARCH_PFN_OFFSET.
    
    The use of ARCH_PFN_OFFSET only affects normal memory and not IO mappings.
    ioremap uses map_page and isn't affected by ARCH_PFN_OFFSET.
    
    /dev/mem continues to allow access to any physical address in the system
    regardless of how CONFIG_PHYSICAL_START is set.
    Signed-off-by: default avatarKumar Gala <galak@kernel.crashing.org>
    Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
    37dd2bad
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