Re: [RFC] MAX_RESERVED_REGIONS hard-coded value

[Miles Chen <miles.chen@mediatek.com>]

Hi,

On Tue, 2020-01-07 at 15:13 -0600, Rob Herring wrote:
> On Mon, Jan 6, 2020 at 12:05 PM Daniele Alessandrelli
> <daniele.alessandrelli@gmail.com> wrote:
> >
> > Hi,
> >
> > I'm using a Device Tree with more then 32 reserved memory regions and
> > I'm seeing the following error while booting the Kernel:
> > [    0.000000] OF: reserved mem: not enough space all defined regions.
> 
> How many do you have? Is that DT available somewhere?
> 
> > My understanding is that this is due to the hard-coded value of
> > MAX_RESERVED_REGIONS in drivers/of/of_reserved_mem.c
> >
> > Googling around, I found this old discussion [1] in which Miles
> > suggests to add a CONFIG_MAX_OF_RESERVED_REGIONS kconfig option to
> > configure MAX_RESERVED_REGIONS. Rob replied to Miles' email saying
> > that he would prefer MAX_RESERVED_REGIONS to be dynamic. However,
> > later in the thread, it looks like making MAX_RESERVED_REGIONS dynamic
> > poses some implementation issues [2]. At that point the discussion
> > seemed to have stopped.
> 
> Not sure what the problem was as there's no code, but I'd guess the
> array alloc and populating have to be done later (perhaps in
> unflattening).

I missed my draft patch.

From what I recall, the problem I had that time is that
early_init_fdt_scan_reserved_mem() is called before paging_init(). So I
cannot allocate accessible memory in early_init_fdt_scan_reserved_mem().

For example: aarch64 setup_arch()
setup_arch()
{
    memblock_init(); /* early_init_fdt_scan_reserved_mem() is called */
    paging_init(); /* map memory */
}

> 
> > Is there any chance for the patch proposed by Miles to be reconsidered?
> 
> A kconfig option would still be my 3rd choice after dynamically
> allocating the array or just growing the fixed array size.

Not sure how many of reserve memory regions Daniele has. In my case,
we grow the MAX_RESERVED_REGIONS to 64 (3x used) and we are still trying
to suppress the amount of reserved memory to fit
MAX_RESERVED_REGIONS=32.



thanks,
Miles
> 
> Rob