From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754900Ab2GJXG7 (ORCPT ); Tue, 10 Jul 2012 19:06:59 -0400 Received: from g1t0027.austin.hp.com ([15.216.28.34]:17756 "EHLO g1t0027.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754170Ab2GJXG6 (ORCPT ); Tue, 10 Jul 2012 19:06:58 -0400 Message-ID: <1341961616.2502.52.camel@lorien2> Subject: Re: [PATCH RFC] swiotlb: Remove SWIOTLB overflow buffer support From: Shuah Khan Reply-To: shuah.khan@hp.com To: Konrad Rzeszutek Wilk Cc: fujita.tomonori@lab.ntt.co.jp, LKML , akpm@linux-foundation.org, paul.gortmaker@windriver.com, bhelgaas@google.com, amwang@redhat.com Date: Tue, 10 Jul 2012 17:06:56 -0600 In-Reply-To: <20120710173211.GB6868@phenom.dumpdata.com> References: <1341615972.3101.27.camel@lorien2> <20120709202505.GA9541@phenom.dumpdata.com> <1341939307.2502.34.camel@lorien2> <20120710173211.GB6868@phenom.dumpdata.com> Organization: ISS-Linux Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2012-07-10 at 13:32 -0400, Konrad Rzeszutek Wilk wrote: > On Tue, Jul 10, 2012 at 10:55:07AM -0600, Shuah Khan wrote: > > On Mon, 2012-07-09 at 16:25 -0400, Konrad Rzeszutek Wilk wrote: > > > On Fri, Jul 06, 2012 at 05:06:12PM -0600, Shuah Khan wrote: > > > > Remove SWIOTLB overflow buffer support and return DMA_ERROR_CODE > > > > (a value of zero) to make it consistent with iommu implementation > > > > on Intel, AMD, and swiotlb-xen. > > > > > > While this is a good forward step and this needs to be done eventually, > > > you should first send out patches for the drivers that don't check > > > for the DMA_ERROR_CODE when doing mapping. In other words for the > > > drivers that map but don't call dma_mapping_error to check. > > > > > > When that is fixed and *all the drivers that don't call dma_mapping_error > > > are fixed, then this patch makes sense. > > > > The challenge will be catching all the drivers and have confidence that > > all of them are covered. I will start looking into this to get a feel > > for how many drivers needs fixing. > > I don't know if all is needed. Some of them might be dead or not used > at all anymore - who knows? This treasure hunt would give a good idea > of which ones are not using the PCI/DMA API right at least. > > If it is say, CONFIG_ISA enabled, well, we could #ifdef the overflow > buffer in the swiotlb with that option. And then work through fixing > up those drivers - except that finding folks with that driver to > see if it works .. yuck.. I do have some few ISA cards and some boxes > with ISA slots :-) Looking at the history CONFIG_ISA was disabled back in 2002 and CONFIG_ISA_DMA_API was disabled in 2004. Sounds like it will be fun finding drivers that could fail. Would it make sense to make io_tlb_overflow a tunable and disable by default instead of ifdef? Currently it is always enabled, disabling it by default is another way to find problems? Good to know you have a few ISA cards. :) -- Shuah