From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King Subject: Re: [PATCH] asm-generic: add dma-mapping-linear.h Date: Mon, 1 Jun 2009 10:22:59 +0100 Message-ID: <20090601092259.GB5550@flint.arm.linux.org.uk> References: <20090601075114.GA29107@flint.arm.linux.org.uk> <20090601170847V.fujita.tomonori@lab.ntt.co.jp> <20090601082943.GA5550@flint.arm.linux.org.uk> <20090601181723U.fujita.tomonori@lab.ntt.co.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from caramon.arm.linux.org.uk ([78.32.30.218]:53911 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755075AbZFAJXN (ORCPT ); Mon, 1 Jun 2009 05:23:13 -0400 Content-Disposition: inline In-Reply-To: <20090601181723U.fujita.tomonori@lab.ntt.co.jp> Sender: linux-arch-owner@vger.kernel.org List-ID: To: FUJITA Tomonori Cc: arnd@arndb.de, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org On Mon, Jun 01, 2009 at 06:16:56PM +0900, FUJITA Tomonori wrote: > On Mon, 1 Jun 2009 09:29:43 +0100 > Russell King wrote: > > > On Mon, Jun 01, 2009 at 05:08:09PM +0900, FUJITA Tomonori wrote: > > > This adds a version of the dma-mapping API to asm-generic that can be > > > used by most architectures that only need a linear mapping. > > > > It depends what is meant by "linear mapping". > > > > If that's just a way of saying "all that needs to be done for the > > DMA streaming APIs is to flush the cache" then the vast majority of > > ARMs fall into that category. > > I guess that his definition is 'no dynamic remapping'. ... which as I say is what ARM does for the streaming mappings. > > The DMA bounce code is a broken design concept that really needs to > > be put to death. > > You are talking about arch/arm/common/dmabounce.c? If so, it sounds > more interesting (to me at least). It's kinda swiotlb per device, > right? What you want to do for arch/arm/common/dmabounce.c? Yes. It's a nasty hack which leads to OOMs on various platforms since it causes additional memory pressure from parts of the kernel which we don't expect, and also causes additional difficulty with allocating and freeing DMA memory from IRQ context. There's an unsolved bug in the kernel bugzilla for this which I see no hope of ever being resolved. I _really_ wish that dmabounce never existed. It's a right royal pain in the preverbial. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: