From db57f88e4ccbbb6dd194b3f3088b3dc1987db423 Mon Sep 17 00:00:00 2001 From: Kevin Cernekee Date: Mon, 10 Aug 2015 20:53:11 +0100 Subject: ARM: 8411/1: Add default SPARSEMEM settings We can still override these settings via mach/memory.h, but let's provide sensible defaults so that SPARSEMEM is available in the multiplatform kernels. Two platforms currently use SECTION_SIZE_BITS < 28, but are expected to work with 28 (albeit slightly less efficiently if not all banks are populated): - mach-rpc: uses 26 bits. Based on mach/hardware.h it looks like this platform puts RAM at 0x1000_0000 - 0x1fff_ffff, and I/O below 0x1000_0000. - mach-sa1100: uses 27 bits. mach/memory.h indicates that RAM occupies the entire range of 0xc000_0000 - 0xdfff_ffff. But Arnd says in that rpc and sa1100 will never have to use the default since they cannot be part of a multiplatform kernel, and that is unlikely to change. Several platforms need MAX_PHYSMEM_BITS >= 36 so we'll pick that as the minimum. Anything higher and we'll fail the SECTIONS_WIDTH + NODES_WIDTH + ZONES_WIDTH test in . Some analysis from Russell King at http://lists.infradead.org/pipermail/linux-arm-kernel/2014-October/298957.html: I think this is fine in as far as it goes - this means we end up with 256 entries in the mem_section array which means it occupies one page, which I think is acceptable overhead. The other thing to be aware of here is the obvious: #if (MAX_ORDER - 1 + PAGE_SHIFT) > SECTION_SIZE_BITS #error Allocator MAX_ORDER exceeds SECTION_SIZE #endif Which means that with 28 bits of section, that's a maximum allocator order of 16. We appear to allow FORCE_MAX_ZONEORDER to be set up to 64 in the case of shmobile, which doesn't seem like a sensible upper limit - and certainly isn't when sparsemem is enabled. Given this, I think that FORCE_MAX_ZONEORDER's help, and the dependencies probably could do with some improvement to make the issues more transparent. [gregory.0xf0: added notes from Arnd and Russell] Signed-off-by: Kevin Cernekee Acked-by: Arnd Bergmann Tested-by: Stephen Boyd Signed-off-by: Gregory Fong Signed-off-by: Russell King --- arch/arm/include/asm/sparsemem.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'arch') diff --git a/arch/arm/include/asm/sparsemem.h b/arch/arm/include/asm/sparsemem.h index 00098615c6f0..73e5e8513751 100644 --- a/arch/arm/include/asm/sparsemem.h +++ b/arch/arm/include/asm/sparsemem.h @@ -15,10 +15,11 @@ * Eg, if you have 2 banks of up to 64MB at 0x80000000, 0x84000000, * then MAX_PHYSMEM_BITS is 32, SECTION_SIZE_BITS is 26. * - * Define these in your mach/memory.h. + * These can be overridden in your mach/memory.h. */ -#if !defined(SECTION_SIZE_BITS) || !defined(MAX_PHYSMEM_BITS) -#error Sparsemem is not supported on this platform +#if !defined(MAX_PHYSMEM_BITS) || !defined(SECTION_SIZE_BITS) +#define MAX_PHYSMEM_BITS 36 +#define SECTION_SIZE_BITS 28 #endif #endif -- cgit v1.2.3