From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mercury.realtime.net (mercury.realtime.net [205.238.132.86]) by ozlabs.org (Postfix) with ESMTP id D1061DDE19 for ; Wed, 26 Nov 2008 04:05:35 +1100 (EST) In-Reply-To: <1227571828.20022.5.camel@localhost> References: <4b6790c7a989dce8c200000687275224@bga.com> <84e16946c1ed4b782568f6492931512a@bga.com> <200811141609.44161.hollisb@us.ibm.com> <1227557235.17746.25.camel@localhost.localdomain> <1227571828.20022.5.camel@localhost> Mime-Version: 1.0 (Apple Message framework v624) Content-Type: text/plain; charset=US-ASCII; format=flowed Message-Id: From: Milton Miller Subject: Re: [PATCH] [v3] powerpc/4xx: work around CHIP11 errata in a more PAGE_SIZE-friendly way Date: Tue, 25 Nov 2008 11:10:38 -0600 To: Hollis Blanchard Cc: linux-ppc , Wolfgang Denk , Ilya Yanok List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Nov 24, 2008, at 6:10 PM, Michael Ellerman wrote: > On Mon, 2008-11-24 at 14:07 -0600, Hollis Blanchard wrote: >> 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 >> --- >> 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; > > All of the current code using memory_limit looks like it'll be safe > with > this change, although there are several cases of this we could remove: > > if (memory_limit && ) > > Because memory_limit will now always be true. memory_limit was the result of parsing mem= from the command line. Does this break that? > > 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. I would have expected this trimming to occur where we actually transfer the memory from lmb to bootmem, since it is bootmem that has the aligned size requirement. milton