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    SubjectRe: [PATCH] WIP: HACK: LPAE, BOOTMEM and NO_BOOTMEM
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    On Sat, Jun 29, 2013 at 10:57 AM, Tejun Heo <tj@kernel.org> wrote:
    > ( Expanding cc list, original thread is at
    > http://thread.gmane.org/gmane.linux.kernel/1518046 )
    >
    > Hello,
    >
    > On Sat, Jun 29, 2013 at 06:21:24PM +0100, Russell King - ARM Linux wrote:
    >> Unfortunately, that has not been true on ARM - it's very common for
    >> there to be an offset on physical memory, sometimes of the order of
    >> 3GB or more. This is because on reset, ARMs start executing the code
    >> at physical address zero, which therefore can't be RAM - and there's
    >> a desire to avoid complex switching games in hardware to temporarily
    >> map ROM there instead of RAM.
    >>
    >> On these SoCs which Santosh is working on, the main physical memory
    >> mapping is above 4GB, with just a small alias below 4GB to allow the
    >> system to boot without the MMU being on, as they may have more than
    >> 4GB of RAM. As I understand it, the small alias below 4GB is not
    >> suitable for use as a "lowmem" mapping.

    is that 32bit ARM or 64bit ARM?

    >
    > Ah, okay, so the @limit which is in physical address can be over 4GB
    > even for lowmem mappings and alloc_bootmem takes them in ulongs,
    > urghhh....
    >
    > Given that still about half of the archs aren't using memblock yet, I
    > think there are three options.
    >
    > 1. Converting all bootmem interface to use physaddr_t. But that's
    > what memblock is.
    >
    > 2. Introducing new interface. Easier right now but the danger there
    > is that it might end up duplicating most of alloc_bootmem()
    > interface anyway and we'll have yet another variant of early mem
    > allocator to enjoy.
    >
    > 3. Make all generic code use memblock interface instead of bootmem and
    > implement memblock wrapper on archs which don't use memblock yet.
    > We'll probably need to sort out different combinations of
    > HAVE_MEMBLOCK and NO_BOOTMEM. If this is doable, it probably is
    > the most future proof way. While it adds new memblock interface
    > built on top of bootmem, it would also allow removing the bootmem
    > interface built on top of memblock - ie. nobootmem.c, which
    > probably is what we should have done from the beginning.
    >
    > What do you guys think?

    2. looks more simple.
    but will use alloc_memblock as interface.

    We don't need to use __alloc_memory_core_early() directly, right?

    Thanks

    Yinghai


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