Messages in this thread | | | Date | Tue, 28 Nov 2006 11:14:44 +0100 | From | "Jesper Juhl" <> | Subject | Re: Reserving a fixed physical address page of RAM. |
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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)
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