From 6c359eb1dcdb721908f4336171ed8eb6d78190c5 Mon Sep 17 00:00:00 2001 From: Paul Burton Date: Fri, 27 Jul 2018 18:23:20 -0700 Subject: 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 Suggested-by: Vladimir Kondratiev Patchwork: https://patchwork.linux-mips.org/patch/20048/ Cc: James Hogan Cc: Ralf Baechle Cc: linux-mips@linux-mips.org --- arch/mips/Kconfig | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/mips/Kconfig') diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig index 10256056647c..fbf7f678e856 100644 --- a/arch/mips/Kconfig +++ b/arch/mips/Kconfig @@ -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" -- cgit v1.2.3