Re: [PATCH v2 4/5] ARM: init: add support for reserved memory defined by device tree

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hello,

On 2014-02-05 11:15, Grant Likely wrote:
> On Tue, 04 Feb 2014 13:09:32 +0100, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> > Enable reserved memory initialization from device tree.
> >
> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Cc: Laura Abbott <lauraa@codeaurora.org>
> > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> > ---
> >  arch/arm/mm/init.c |    3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> > index 804d61566a53..ebafdb479410 100644
> > --- a/arch/arm/mm/init.c
> > +++ b/arch/arm/mm/init.c
> > @@ -17,6 +17,7 @@
> >  #include <linux/nodemask.h>
> >  #include <linux/initrd.h>
> >  #include <linux/of_fdt.h>
> > +#include <linux/of_reserved_mem.h>
> >  #include <linux/highmem.h>
> >  #include <linux/gfp.h>
> >  #include <linux/memblock.h>
> > @@ -323,6 +324,8 @@ void __init arm_memblock_init(struct meminfo *mi,
> >  	if (mdesc->reserve)
> >  		mdesc->reserve();
> >
> > +	early_init_dt_scan_reserved_mem();
> > +
>
> The new binding is being made fundamental. If the reserved-memory node
> is present, then it needs to be honored, even if the kernel doesn't know
> how to use the regions. Therefore, This needs to be unconditional for
> all architectures. The hook should be called in early_init_dt_scan()
> (drivers/of/fdt.c) immediately after the early_init_dt_scan_memory()
> hook.

In theory this will be the best solution, but it practice there is a
problem. early_init_dt_scan() is called as the first function from kernel
booting code. That time there is no memory yet added to the system, so it
would be really hard to reserve anything. Memory nodes are being added
later either with memblock_add() or by some other arch specific way.

Finally, once all memory has been added to the system we can parse and
reserve all regions defined in the device tree. This really requires
creating another function which will be called by arch specific code.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland