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

From: Hollis Blanchard <[email-masked]>
Date: Mon, 24 Nov 2008 14:07:15 -0600

On Fri, 2008-11-14 at 16:09 -0600, Hollis Blanchard wrote:
> 
> If this is all too much, then I'm close to giving up and burning a
> 64KB page, which requires only ALIGN_DOWN() in the kernel.

ppc: force memory size to be a multiple of PAGE_SIZE

Ensure that total memory size is page-aligned, because otherwise
bootmem.c gets upset.

This error case was triggered by using 64 KiB pages in the kernel while
arch/powerpc/boot/4xx.c arbitrarily reduced the amount of memory by 4096 (to
work around the "CHIP11" errata which affects the last 256 bytes of physical memory).

Signed-off-by: Hollis Blanchard <[email-masked]>
---
This is on a common code path, and lmb_enforce_memory_limit() will now
always take action, so wider testing would be good.

This patch supercedes http://patchwork.ozlabs.org/patch/8211/ .

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -1200,6 +1200,11 @@ void __init early_init_devtree(void *par
 	early_reserve_mem();
 	phyp_dump_reserve_mem();
 
+	/* Ensure that total memory size is page-aligned, because otherwise
+	 * bootmem.c gets upset. */
+	lmb_analyze();
+	memory_limit = lmb_phys_mem_size() & PAGE_MASK;
+
 	lmb_enforce_memory_limit(memory_limit);
 	lmb_analyze();
 
-- 
Hollis Blanchard
IBM Linux Technology Center