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

From: Michael Ellerman <[email-masked]>
Date: Wed, 26 Nov 2008 10:43:51 +1100

On Tue, 2008-11-25 at 15:53 -0600, Hollis Blanchard wrote:
> On Tue, 2008-11-25 at 11:10 +1100, Michael Ellerman wrote:
> > 
> > Still, I think it would be better to only set memory_limit when the mem
> > size is not a multiple of the PAGE_SIZE - so that memory_limit retains
> > it's function as both the value of the limit and a boolean.
> 
> OK, how's this?
> 
> ppc: force memory size to be a multiple of PAGE_SIZE
> 
> Ensure that total memory size is page-aligned, because otherwise
> mark_bootmem() 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 a chip bug that affects the last 256 bytes of physical memory).
> 
> Signed-off-by: Hollis Blanchard <[email-masked]>
> 
> 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
> @@ -1160,6 +1160,8 @@ static inline void __init phyp_dump_rese
>  
>  void __init early_init_devtree(void *params)
>  {
> +	unsigned long limit, memsize;
> +
>  	DBG(" -> early_init_devtree(%p)\n", params);
>  
>  	/* Setup flat device-tree pointer */
> @@ -1200,7 +1202,15 @@ void __init early_init_devtree(void *par
>  	early_reserve_mem();
>  	phyp_dump_reserve_mem();

I was thinking more like the following:

>  
> -	lmb_enforce_memory_limit(memory_limit);
> +	limit = memory_limit;
> +	if (! limit) {
> +		/* Ensure that total memory size is page-aligned, because
> +		 * otherwise mark_bootmem() gets upset. */
> +		lmb_analyze();
                  memsize = lmb_phys_mem_size();
		  if(memsize & PAGE_MASK != memsize)
		        limit = memsize & PAGE_MASK;
> +	}
> +	lmb_enforce_memory_limit(limit);
> +

So that we never needlessly run through the enforce code with limit =
memsize. But maybe it's a bit pedantic.

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person