linux/arch/arc
Vineet Gupta 26f9d5fd82 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 <noamc@ezchip.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
2016-05-05 16:35:46 +05:30
..
boot Revert "ARC: [plat-axs10x] add Ethernet PHY description in .dts" 2016-04-07 14:59:09 +05:30
configs ARC: [plat-axs103] Enable loop block devices 2016-04-07 14:59:09 +05:30
include ARC: support HIGHMEM even without PAE40 2016-05-05 16:35:46 +05:30
kernel ARCv2: Enable LOCKDEP 2016-04-22 18:12:31 +05:30
lib ARCv2: lib: memcpy: use local symbols 2015-11-03 17:33:00 +05:30
mm ARC: support HIGHMEM even without PAE40 2016-05-05 16:35:46 +05:30
oprofile ARC: OProfile support 2013-02-15 23:16:00 +05:30
plat-axs10x ARC: Add PCI support 2016-03-10 14:44:13 -06:00
plat-sim ARC: remove extraneous header include 2015-11-14 13:11:38 +05:30
plat-tb10x ARC: [plat*] move code out of .init_machine into common 2014-10-13 14:46:13 +05:30
Kbuild
Kconfig ARC: support HIGHMEM even without PAE40 2016-05-05 16:35:46 +05:30
Kconfig.debug ARC: With earlycon in use, retire EARLY_PRINTK 2015-05-11 11:20:21 +05:30
Makefile ARC: build: Turn off -Wmaybe-uninitialized for ARC gcc 4.8 2016-03-18 16:22:36 +05:30