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    MIPS: Allow auto-dection of ARCH_PFN_OFFSET & PHYS_OFFSET · 6c359eb1
    Paul Burton 提交于
    On systems where physical memory begins at a non-zero address, defining
    PHYS_OFFSET (which influences ARCH_PFN_OFFSET) can save us time & memory
    by avoiding book-keeping for pages from address zero to the start of
    memory.
    
    Some MIPS platforms already make use of this, but with the definition of
    PHYS_OFFSET being compile-time constant it hasn't been possible to
    enable this optimization for a kernel which may run on systems with
    varying physical memory base addresses.
    
    Introduce a new Kconfig option CONFIG_MIPS_AUTO_PFN_OFFSET which, when
    enabled, makes ARCH_PFN_OFFSET a variable & detects it from the boot
    memory map (which for example may have been populated from DT). The
    relationship with PHYS_OFFSET is reversed, with PHYS_OFFSET now being
    based on ARCH_PFN_OFFSET. This is because ARCH_PFN_OFFSET is used far
    more often, so avoiding the need for runtime calculation gives us a
    smaller impact on kernel text size (0.1% rather than 0.15% for
    64r6el_defconfig).
    Signed-off-by: NPaul Burton <paul.burton@mips.com>
    Suggested-by: NVladimir Kondratiev <vladimir.kondratiev@intel.com>
    Patchwork: https://patchwork.linux-mips.org/patch/20048/
    Cc: James Hogan <jhogan@kernel.org>
    Cc: Ralf Baechle <ralf@linux-mips.org>
    Cc: linux-mips@linux-mips.org
    6c359eb1
Kconfig 79.8 KB