From 26f9d5fd82ca20fe536cb493ec7cf5628f8997e5 Mon Sep 17 00:00:00 2001 From: Vineet Gupta Date: Mon, 18 Apr 2016 10:49:56 +0530 Subject: ARC: support HIGHMEM even without PAE40 Initial HIGHMEM support on ARC was introduced for PAE40 where the low memory (0x8000_0000 based) and high memory (0x1_0000_0000) were physically contiguous. So CONFIG_FLATMEM sufficed (despite a peipheral hole in the middle, which wasted a bit of struct page memory, but things worked). However w/o PAE, highmem was not possible and we could only reach ~1.75GB of DDR. Now there is a use case to access ~4GB of DDR w/o PAE40 The idea is to have low memory at canonical 0x8000_0000 and highmem at 0 so enire 4GB address space is available for physical addressing This needs additional platform/interconnect mapping to convert the non contiguous physical addresses into linear bus adresses. From Linux point of view, non contiguous divide means FLATMEM no longer works and DISCONTIGMEM is needed to track the pfns in the 2 regions. This scheme would also work for PAE40, only better in that we don't waste struct page memory for the peripheral hole. The DT description will be something like memory { ... reg = <0x80000000 0x200000000 /* 512MB: lowmem */ 0x00000000 0x10000000>; /* 256MB: highmem */ } Signed-off-by: Noam Camus Signed-off-by: Vineet Gupta --- arch/arc/Kconfig | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'arch/arc/Kconfig') diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig index ec4791ea6911..a8767430df7d 100644 --- a/arch/arc/Kconfig +++ b/arch/arc/Kconfig @@ -58,6 +58,9 @@ config GENERIC_CSUM config RWSEM_GENERIC_SPINLOCK def_bool y +config ARCH_DISCONTIGMEM_ENABLE + def_bool y + config ARCH_FLATMEM_ENABLE def_bool y @@ -347,6 +350,15 @@ config ARC_HUGEPAGE_16M endchoice +config NODES_SHIFT + int "Maximum NUMA Nodes (as a power of 2)" + default "1" if !DISCONTIGMEM + default "2" if DISCONTIGMEM + depends on NEED_MULTIPLE_NODES + ---help--- + Accessing memory beyond 1GB (with or w/o PAE) requires 2 memory + zones. + if ISA_ARCOMPACT config ARC_COMPACT_IRQ_LEVELS @@ -455,6 +467,7 @@ config LINUX_LINK_BASE config HIGHMEM bool "High Memory Support" + select DISCONTIGMEM help With ARC 2G:2G address split, only upper 2G is directly addressable by kernel. Enable this to potentially allow access to rest of 2G and PAE -- cgit v1.2.3