[PATCH v2 3/4] ARM: mm: truncate memory banks to fit in 4GB space for classic MMU

[Russell King - ARM Linux]

On Wed, Apr 11, 2012 at 04:52:32PM +0100, Russell King - ARM Linux wrote:
> On Wed, Apr 11, 2012 at 10:44:22AM -0400, Nicolas Pitre wrote:
> > On Wed, 11 Apr 2012, Will Deacon wrote:
> > 
> > > If a bank of memory spanning the 4GB boundary is added on a !CONFIG_LPAE
> > > kernel then we will hang early during boot since the memory bank will
> > > have wrapped around to zero.
> > > 
> > > This patch truncates memory banks for !LPAE configurations when the end
> > > address is not representable in 32 bits.
> > > 
> > > Cc: Nicolas Pitre <nico at fluxnic.net>
> > > Signed-off-by: Will Deacon <will.deacon at arm.com>
> > 
> > Acked-by: Nicolas Pitre <nico at linaro.org>
> > 
> > Now what if start = 1G and size = 5G? The size variable is an unsigned 
> > long, meaning that right now the size might be truncated to 1G.
> 
> There's a solution to that which is quite easy to do: convert the bank
> information to PFNs instead of addresses.  That will probably eliminate
> some corner cases with partial pages which would be desirable too.

Of course, what prevents us doing that conversion sanely is all the
shite platform code doing crap stuff like this:

arch/arm/mach-msm/board-halibut.c:      mi->bank[0].start = PHYS_OFFSET;
arch/arm/mach-msm/board-halibut.c:      mi->bank[0].size = (101*1024*1024);

which I went through everything a few years ago and eliminated all this
crap.  It's back now.  Sod it, we'll stick with the current 4GiB limited
way as long as we have platform maintainers who do this kind of crappy
hack.

While here, I propose to delete these:

arch/arm/mach-msm/board-mahimahi.c:     mi->bank[0].start = PHYS_OFFSET;
arch/arm/mach-msm/board-mahimahi.c:     mi->bank[0].node = PHYS_TO_NID(PHYS_OFFSET);
arch/arm/mach-msm/board-mahimahi.c:     mi->bank[0].size = (219*1024*1024);
arch/arm/mach-msm/board-mahimahi.c:     mi->bank[1].start = MSM_HIGHMEM_BASE;
arch/arm/mach-msm/board-mahimahi.c:     mi->bank[1].node = PHYS_TO_NID(MSM_HIGHMEM_BASE);
arch/arm/mach-msm/board-mahimahi.c:     mi->bank[1].size = MSM_HIGHMEM_SIZE;
arch/arm/mach-msm/board-sapphire.c:     mi->bank[0].start = PHYS_OFFSET;
arch/arm/mach-msm/board-sapphire.c:     mi->bank[0].node = PHYS_TO_NID(PHYS_OFFSET);
arch/arm/mach-msm/board-sapphire.c:             mi->bank[0].size = (84*1024*1024);
arch/arm/mach-msm/board-sapphire.c:             mi->bank[0].size = (101*1024*1024);
arch/arm/mach-msm/board-sapphire.c:             mi->bank[0].size = (101*1024*1024);

because they haven't been buildable since 7th May 2010 (that's 23 months
ago), and no one has reported any build errors with them.  They're only
receiving updates from other sweeps and nothing more.  This all means no
one is even attempting to build this code.  It's pointless having
unbuildable code in the kernel, and it's nothing more than a useless
maintanence burden.