From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750863AbeESFZp (ORCPT ); Sat, 19 May 2018 01:25:45 -0400 Received: from kvm5.telegraphics.com.au ([98.124.60.144]:44806 "EHLO kvm5.telegraphics.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750769AbeESFZo (ORCPT ); Sat, 19 May 2018 01:25:44 -0400 Date: Sat, 19 May 2018 15:25:39 +1000 (AEST) From: Finn Thain To: Christoph Hellwig cc: Geert Uytterhoeven , linux-m68k@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Greg Ungerer Subject: Re: [PATCH 1/2] m68k: Set default dma mask for platform devices In-Reply-To: <20180518090434.GC24436@lst.de> Message-ID: References: <20180518090434.GC24436@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 18 May 2018, Christoph Hellwig wrote: > > This implementation of arch_setup_pdev_archdata() differs from the > > powerpc one, in that this one avoids clobbering a device dma mask > > which has already been initialized. > > I think your implementation should move into the generic implementation > in drivers/base/platform.c instead of being stuck in m68k. > > Also powerpc probably wants fixing, but that's something left to the > ppc folks.. On powerpc, all platform devices get a dma mask. But they don't do that in drivers/base/platform.c, they use arch_setup_pdev_archdata(). Why didn't they take the approach you suggest? How would I support the claim that replacing an empty platform device dma mask with 0xffffffff is safe on all architectures and platforms? Is there no code conditional upon dev.coherent_dma_mask or dev.dma_mask that could misbehave? (Didn't I cite an example in the other thread?*) If you can convince me that it is safe, I'd be happy to submit the patch you asked for. For now, I still think that patching the platform driver was the correct patch*. Maybe the real problem is your commit 205e1b7f51e4 ("dma-mapping: warn when there is no coherent_dma_mask"), because it assumes that all dma_ops implementations care about coherent_dma_mask. The dma_map_ops implementations that do use coherent_dma_mask should simply fail when it is unset, right? Would it not be better to revert your patch and fix the dma_map_ops failure paths, than to somehow audit all the platform drivers and patch drivers/base/platform.c? Thanks. * https://lkml.kernel.org/r/alpine.LNX.2.21.1805091804290.72%40nippy.intranet --