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MIPS: Allow auto-dection of ARCH_PFN_OFFSET & PHYS_OFFSET

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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: Paul Burton <paul.burton@mips.com>
Suggested-by: Vladimir 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
This commit is contained in:
Paul Burton
2018-07-27 18:23:20 -07:00
parent 0494d7ffdc
commit 6c359eb1dc
4 changed files with 28 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
arch/mips/include/asm/mach-generic/spaces.h
View File

@@ -17,9 +17,13 @@
/*
* This gives the physical RAM offset.
*/
#ifndef PHYS_OFFSET
#define PHYS_OFFSET _AC(0, UL)
#endif
#ifndef __ASSEMBLY__
# if defined(CONFIG_MIPS_AUTO_PFN_OFFSET)
# define PHYS_OFFSET ((unsigned long)PFN_PHYS(ARCH_PFN_OFFSET))
# elif !defined(PHYS_OFFSET)
# define PHYS_OFFSET _AC(0, UL)
# endif
#endif /* __ASSEMBLY__ */
#ifdef CONFIG_32BIT
#ifdef CONFIG_KVM_GUEST

7
arch/mips/include/asm/page.h
View File

@@ -80,7 +80,12 @@ extern void build_copy_page(void);
* used in our early mem init code for all memory models.
* So always define it.
*/
#define ARCH_PFN_OFFSET PFN_UP(PHYS_OFFSET)
#ifdef CONFIG_MIPS_AUTO_PFN_OFFSET
extern unsigned long ARCH_PFN_OFFSET;
# define ARCH_PFN_OFFSET ARCH_PFN_OFFSET
#else
# define ARCH_PFN_OFFSET PFN_UP(PHYS_OFFSET)
#endif
extern void clear_page(void * page);
extern void copy_page(void * to, void * from);