From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A1011C0044C for ; Wed, 31 Oct 2018 16:31:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 44B9420821 for ; Wed, 31 Oct 2018 16:31:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 44B9420821 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-mips.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729694AbeKABa2 (ORCPT ); Wed, 31 Oct 2018 21:30:28 -0400 Received: from eddie.linux-mips.org ([148.251.95.138]:43146 "EHLO cvs.linux-mips.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726720AbeKABa1 (ORCPT ); Wed, 31 Oct 2018 21:30:27 -0400 Received: (from localhost user: 'macro', uid#1010) by eddie.linux-mips.org with ESMTP id S23991025AbeJaQbkPiy6m (ORCPT ); Wed, 31 Oct 2018 17:31:40 +0100 Date: Wed, 31 Oct 2018 16:31:40 +0000 (GMT) From: "Maciej W. Rozycki" 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 Subject: Re: [PATCH 4/6] dma-mapping: merge direct and noncoherent ops In-Reply-To: Message-ID: References: <20180914095808.22202-1-hch@lst.de> <20180914095808.22202-5-hch@lst.de> User-Agent: Alpine 2.21 (LFD 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 31 Oct 2018, Maciej W. Rozycki 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. Doh! It would have helped if I actually had the right adapter installed in the R3400 box. I've got a spare one, which I have now plugged in there and the R3400 actually shows the same issue as the R4400SC does. So this has nothing to do WRT write-through vs write-back. Hmm, in `dfx_hw_dma_cmd_req' the driver polls the consumer block (which is write-only by the adapter and read-only by the host, except for the initialisation time before adapter's DMA engines have been started, and write-through vs write-back indeed does not matter for this kind of use) and there's no DMA synchronisation whatsoever in that. However the block has been allocated with `dma_zalloc_coherent', which means no synchronisation is supposed to be required. For non-coherent cache systems that essentially means an uncached memory allocation. Maciej