On Sat, Jun 29, 2013 at 10:57 AM, Tejun Heo <tj@xxxxxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
