Re: [PATCH] [v3] powerpc/4xx: work around CHIP11 errata in a more PAGE_SIZE-friendly way

[Josh Boyer <jwboyer@linux.vnet.ibm.com>]

On Wed, 12 Nov 2008 15:37:43 +1100
Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> On Tue, 2008-11-11 at 18:06 -0600, Hollis Blanchard wrote:
> > The current CHIP11 errata truncates the device tree memory node, and subtracts
> > (hardcoded) 4096 bytes. This breaks kernels with larger PAGE_SIZE, since the
> > bootmem allocator assumes that total memory is a multiple of PAGE_SIZE.
> > 
> > Instead, use a device tree memory reservation to reserve only the 256 bytes
> > actually affected by the errata, leaving the total memory size unaltered.
> > 
> > Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
> 
> While I prefer this approach, won't it break kexec ?

Break it how?  Particularly given that kexec doesn't work on 4xx (yet).

> I don't understand why we don't just have a bit of code in the kernel
> itself that reserve that page on 44x at boot time and be done with it.
> 
> It's like we are trying to be too smart and over-engineer the solution.

I don't think that's it.  I think it's more that we're opportunistic and
the wrapper is the easiest place to do this, given that U-Boot itself
will be doing the reserve for platforms that don't require the
wrapper.

So we could do the fixup in-kernel, but how do you do that
deterministically given that U-Boot might have already done it?

josh