From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Maciej W. Rozycki" Subject: Re: [PATCH 4/6] dma-mapping: merge direct and noncoherent ops Date: Wed, 31 Oct 2018 14:24:13 +0000 (GMT) Message-ID: References: <20180914095808.22202-1-hch@lst.de> <20180914095808.22202-5-hch@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: <20180914095808.22202-5-hch@lst.de> Sender: linux-kernel-owner@vger.kernel.org To: Christoph Hellwig Cc: iommu@lists.linux-foundation.org, Marek Szyprowski , Robin Murphy , Paul Burton , Greg Kroah-Hartman , linux-mips@linux-mips.org, linux-kernel@vger.kernel.org List-Id: iommu@lists.linux-foundation.org Hi Christoph, On Fri, 14 Sep 2018, Christoph Hellwig wrote: > All the cache maintainance is already stubbed out when not enabled, > but merging the two allows us to nicely handle the case where > cache maintainance is required for some devices, but not others. FYI, you commit bc3ec75de545 ("dma-mapping: merge direct and noncoherent ops") has caused: fddi0: DMA command request failed! fddi0: Adapter open failed! with the `defxx' driver on my R4400SC TURBOchannel DECstation (but not the R3400 one) and consequently the interface does not work anymore. Both are non-coherent cache systems, however the R3400 implements the write-through policy while the policy of the R4400SC is write-back (it also has 1MiB of secondary cache), which I suspect is the reason of the difference. I'll be experimenting with this commit to figure out what the real cause is, but it'll take a while as my resources are limited, so I'm sending this early heads-up in case you or someone else has an idea what might be going wrong here. Maciej