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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: 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
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commit
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4 changed files with 28 additions and 6 deletions
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@ -2985,6 +2985,9 @@ config PGTABLE_LEVELS
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default 3 if 64BIT && !PAGE_SIZE_64KB
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default 2
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config MIPS_AUTO_PFN_OFFSET
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bool
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source "init/Kconfig"
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source "kernel/Kconfig.freezer"
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@ -17,9 +17,13 @@
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/*
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* This gives the physical RAM offset.
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*/
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#ifndef PHYS_OFFSET
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#define PHYS_OFFSET _AC(0, UL)
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#endif
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#ifndef __ASSEMBLY__
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# if defined(CONFIG_MIPS_AUTO_PFN_OFFSET)
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# define PHYS_OFFSET ((unsigned long)PFN_PHYS(ARCH_PFN_OFFSET))
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# elif !defined(PHYS_OFFSET)
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# define PHYS_OFFSET _AC(0, UL)
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# endif
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#endif /* __ASSEMBLY__ */
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#ifdef CONFIG_32BIT
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#ifdef CONFIG_KVM_GUEST
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@ -80,7 +80,12 @@ extern void build_copy_page(void);
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* used in our early mem init code for all memory models.
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* So always define it.
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*/
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#define ARCH_PFN_OFFSET PFN_UP(PHYS_OFFSET)
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#ifdef CONFIG_MIPS_AUTO_PFN_OFFSET
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extern unsigned long ARCH_PFN_OFFSET;
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# define ARCH_PFN_OFFSET ARCH_PFN_OFFSET
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#else
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# define ARCH_PFN_OFFSET PFN_UP(PHYS_OFFSET)
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#endif
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extern void clear_page(void * page);
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extern void copy_page(void * to, void * from);
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@ -85,6 +85,11 @@ static struct resource bss_resource = { .name = "Kernel bss", };
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static void *detect_magic __initdata = detect_memory_region;
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#ifdef CONFIG_MIPS_AUTO_PFN_OFFSET
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unsigned long ARCH_PFN_OFFSET;
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EXPORT_SYMBOL(ARCH_PFN_OFFSET);
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#endif
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void __init add_memory_region(phys_addr_t start, phys_addr_t size, long type)
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{
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int x = boot_mem_map.nr_map;
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@ -442,6 +447,12 @@ static void __init bootmem_init(void)
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mapstart = max(reserved_end, start);
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}
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if (min_low_pfn >= max_low_pfn)
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panic("Incorrect memory mapping !!!");
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#ifdef CONFIG_MIPS_AUTO_PFN_OFFSET
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ARCH_PFN_OFFSET = PFN_UP(ramstart);
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#else
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/*
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* Reserve any memory between the start of RAM and PHYS_OFFSET
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*/
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@ -449,8 +460,6 @@ static void __init bootmem_init(void)
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add_memory_region(PHYS_OFFSET, ramstart - PHYS_OFFSET,
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BOOT_MEM_RESERVED);
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if (min_low_pfn >= max_low_pfn)
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panic("Incorrect memory mapping !!!");
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if (min_low_pfn > ARCH_PFN_OFFSET) {
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pr_info("Wasting %lu bytes for tracking %lu unused pages\n",
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(min_low_pfn - ARCH_PFN_OFFSET) * sizeof(struct page),
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@ -460,6 +469,7 @@ static void __init bootmem_init(void)
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ARCH_PFN_OFFSET - min_low_pfn);
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}
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min_low_pfn = ARCH_PFN_OFFSET;
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#endif
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/*
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* Determine low and high memory ranges
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