Messages in this thread | | | Subject | RE: Reserving a fixed physical address page of RAM. | Date | Tue, 28 Nov 2006 14:37:32 -0500 | From | "Jon Ringle" <> |
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Jesper Juhl wrote: > On 28/11/06, Fawad Lateef <fawadlateef@gmail.com> wrote: > > On 11/28/06, Dave Airlie <airlied@gmail.com> wrote: > > > On 11/28/06, Jon Ringle <jringle@vertical.com> wrote: > > <snip> > > > > It looks promising, however, I need to reserve a > physical address > > > > area that is well known (so that the code running on the other > > > > processor knows where in PCI memory to write to). It > appears that > > > > dma_alloc_coherent returns the address that it > allocated. Instead > > > > I need something where I can tell it what physical > address and range I want to use. > > > > > > > > > > I've seen other projects just boot a 128M board with mem=120M and > > > just use the 8MB at 120 to talk to the other processor.. > > > > > > > Yes, this can be used if required physical-memory exists in > the last > > part of RAM as if you use mem=<xxxM> then kernel will only > use memory > > less than or equal-to <xxxM> and above can be used by > drivers (or any > > kernel module) might be through ioremap which takes > physical-address. > > > > But if lets say we need only 1MB portion of specific > physical-memory > > region then AFAIK it must be done by hacking in kernel code during > > memory-initialization (mem_init function) where it is > marking/checking > > pages as/are reserved; you can simply mark you required pages as > > reserved too and set their count to some-value if you want to know > > later which pages are reserved by you. (can do this reservation work > > here: http://lxr.free-electrons.com/source/arch/i386/mm/init.c#605). > > CMIIW > > > > Can you not use the 'memmap=' kernel option to reserve the > specific area you need? > (See Documentation/kernel-parameters.txt for details)
This looks like what I want, but after searching for this, I found that memmap= is implemented for i386 and ia64 only. My arch is arm (processor is an IXP455).
I'll explore the mem= option to see if it will work out.
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