Unverified Commit 6c359eb1 authored by Paul Burton's avatar Paul Burton
Browse files

MIPS: Allow auto-dection of ARCH_PFN_OFFSET & PHYS_OFFSET 



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: default avatarPaul Burton <paul.burton@mips.com>
Suggested-by: default avatarVladimir 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
parent 0494d7ff

arch/mips/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -2985,6 +2985,9 @@ config PGTABLE_LEVELS 
	default 3 if 64BIT && !PAGE_SIZE_64KB

	default 2



config MIPS_AUTO_PFN_OFFSET

	bool



source "init/Kconfig"



source "kernel/Kconfig.freezer"

arch/mips/include/asm/mach-generic/spaces.h

+7 −3
Original line number Diff line number Diff line
@@ -17,9 +17,13 @@ 
/*

 * This gives the physical RAM offset.

 */

#ifndef PHYS_OFFSET

#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

arch/mips/include/asm/page.h

+6 −1
Original line number Diff line number Diff line
@@ -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.

 */

#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);

arch/mips/kernel/setup.c

+12 −2
Original line number Diff line number Diff line
@@ -85,6 +85,11 @@ static struct resource bss_resource = { .name = "Kernel bss", }; 


static void *detect_magic __initdata = detect_memory_region;



#ifdef CONFIG_MIPS_AUTO_PFN_OFFSET

unsigned long ARCH_PFN_OFFSET;

EXPORT_SYMBOL(ARCH_PFN_OFFSET);

#endif



void __init add_memory_region(phys_addr_t start, phys_addr_t size, long type)

{

	int x = boot_mem_map.nr_map;
@@ -442,6 +447,12 @@ static void __init bootmem_init(void) 
		mapstart = max(reserved_end, start);

	}



	if (min_low_pfn >= max_low_pfn)

		panic("Incorrect memory mapping !!!");



#ifdef CONFIG_MIPS_AUTO_PFN_OFFSET

	ARCH_PFN_OFFSET = PFN_UP(ramstart);

#else

	/*

	 * Reserve any memory between the start of RAM and PHYS_OFFSET

	 */
@@ -449,8 +460,6 @@ static void __init bootmem_init(void) 
		add_memory_region(PHYS_OFFSET, ramstart - PHYS_OFFSET,

				  BOOT_MEM_RESERVED);



	if (min_low_pfn >= max_low_pfn)

		panic("Incorrect memory mapping !!!");

	if (min_low_pfn > ARCH_PFN_OFFSET) {

		pr_info("Wasting %lu bytes for tracking %lu unused pages\n",

			(min_low_pfn - ARCH_PFN_OFFSET) * sizeof(struct page),
@@ -460,6 +469,7 @@ static void __init bootmem_init(void) 
			ARCH_PFN_OFFSET - min_low_pfn);

	}

	min_low_pfn = ARCH_PFN_OFFSET;

#endif



	/*

	 * Determine low and high memory ranges

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