From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from quartz.orcorp.ca (quartz.orcorp.ca [184.70.90.242]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 82BC12C034F for ; Fri, 5 Oct 2012 03:08:48 +1000 (EST) Date: Thu, 4 Oct 2012 11:08:41 -0600 From: Jason Gunthorpe To: Benjamin Herrenschmidt Subject: Re: [PATCH] PPC: Correct the tophys/tovirt macros Message-ID: <20121004170841.GA2994@obsidianresearch.com> References: <20120930232847.GG30637@obsidianresearch.com> <1349349544.4260.24.camel@pasglop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1349349544.4260.24.camel@pasglop> Cc: linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, Oct 04, 2012 at 09:19:04PM +1000, Benjamin Herrenschmidt wrote: > On Sun, 2012-09-30 at 17:28 -0600, Jason Gunthorpe wrote: > > asm/page.h discusses the calculation for v2p and p2v, it should be: > > va = pa + KERNELBASE - PHYSICAL_START > > which is the same as: > > va = pa + LOAD_OFFSET > > > > tophys/tovirt were using PAGE_OFFSET, which as page.h says, is almost > > always the same thing. > > > > Signed-off-by: Jason Gunthorpe > > It's a bit gross tho in that KERNEL_BASE, PHYSICAL_START and LOAD_OFFSET > are about where the kernel is linked/running, and while the value ends > up happening to also be the p->v offset (and indeed not by accident), it > makes the code less clear and more confusing. Yes, I found the three names confusing.. However LOAD_OFFSET is the name that include/asm-generic/vmlinux.lds.h and many arch's use for P2V translation in the linker script, so at least there is some precedent. > I don't have the bandwidth to revisit all that, but I really think that > whole are area where PAGE_OFFSET doesn't map 0 needs revisiting. Something like that is also outside my scope.. This patch does fix a bug I hit when CONFIG_PHYSICAL_START is used, are there problems with it in other cases? FWIW, this is part of a larger work that makes CONFIG_PHYSICAL_START work on PPC404, which is not yet clean enough to post: https://github.com/jgunthorpe/linux/commit/90df2d247c9db5d39c32dbbada0815f15d7b3be7 Regards, Jason