On 11/30/06, Jon Ringle <[email protected]> wrote:
Fawad Lateef wrote:
> On 11/30/06, Jon Ringle <[email protected]> wrote:
> > Fawad Lateef wrote:
> > > 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.
> >
> > Seems that using mem= has to be in 1MB increments, where I
> only need 4K.
> >
>
> No AFAIK you can specify it in KBs (see
> http://sosdg.org/~coywolf/lxr/source/Documentation/kernel-para
> meters.txt#L869)
Yes, you can specify the mem= using K notation, but there is a test in
arch/arm/mm/mm-armv.c:create_mapping() that prevents the mapping from
being created if the boundaries are not MB aligned:
if (mem_types[md->type].prot_l1 == 0 &&
(virt & 0xfffff || (virt + off) & 0xfffff || (virt + length)
& 0xfffff)) {
printk(KERN_WARNING "BUG: map for 0x%08lx at 0x%08lx can
not "
"be mapped using pages, ignoring.\n",
__pfn_to_phys(md->pfn), md->virtual);
return;
}
This is in linux-2.6.16.29.
Ohh ok, I don't know about this architecture related information.
>
> > >
> > > 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).
> >
> > Do you think that the following would work to properly reserve the
> > memory. If it does, then I think I can just do a ioremap(0x0ffff000,
> > 0x1000) to obtain a virtual address. (Ofcourse I would actually use
> > symbolic names rather than the hardcoded addesses shown here).
> >
> > Index: linux/arch/arm/mm/init.c
> > ===================================================================
> > --- linux.orig/arch/arm/mm/init.c 2006-11-30
> 11:03:00.000000000
> > -0500
> > +++ linux/arch/arm/mm/init.c 2006-11-30 11:09:09.000000000 -0500
> > @@ -429,6 +429,10 @@
> > unsigned long addr;
> > void *vectors;
> >
> > +#ifdef CONFIG_MACH_VERTICAL_RSC4
> > + reserve_bootmem (0x0ffff000, 0x1000); #endif
> > +
> > /*
> > * Allocate the vector page early.
> > */
> >
> >
>
> I think you can do like this but can't say accurately because
> I havn't worked on arm architecture and also you havn't
> mentioned your kernel-version or function (in file
> arch/arm/mm/init.c) which you are going to do call reserve_bootmem !
Kernel version is 2.6.16.29 and the reserve_bootmem() call above is at
the top of the function devicemaps_init().
reserving_bootmem in devicemaps_init will work but I think it will be
better if you do this in mem_init function (here:
http://sosdg.org/~coywolf/lxr/source/arch/arm/mm/init.c?v=2.6.16;a=arm#L620),
so that all the paging and other map related stuff completes. (CMIIW)
--
Fawad Lateef
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