From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752797AbdFRJz5 (ORCPT ); Sun, 18 Jun 2017 05:55:57 -0400 Received: from gate.crashing.org ([63.228.1.57]:57180 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751009AbdFRJzx (ORCPT ); Sun, 18 Jun 2017 05:55:53 -0400 Message-ID: <1497779642.31581.6.camel@kernel.crashing.org> Subject: Re: [PATCH 42/44] powerpc/cell: use the dma_supported method for ops switching From: Benjamin Herrenschmidt To: Christoph Hellwig Cc: Christoph Hellwig , x86@kernel.org, linux-arm-kernel@lists.infradead.org, xen-devel@lists.xenproject.org, linux-c6x-dev@linux-c6x.org, linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org, linux-mips@linux-mips.org, openrisc@lists.librecores.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, dmaengine@vger.kernel.org, linux-tegra@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-samsung-soc@vger.kernel.org, iommu@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Sun, 18 Jun 2017 19:54:02 +1000 In-Reply-To: <20170618071344.GB18526@infradead.org> References: <20170616181059.19206-1-hch@lst.de> <20170616181059.19206-43-hch@lst.de> <1497732627.2897.128.camel@kernel.crashing.org> <20170618071344.GB18526@infradead.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-2.fc25) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2017-06-18 at 00:13 -0700, Christoph Hellwig wrote: > On Sun, Jun 18, 2017 at 06:50:27AM +1000, Benjamin Herrenschmidt wrote: > > What is your rationale here ? (I have missed patch 0 it seems). > > Less code duplication, more modular dma_map_ops insteance. > > > dma_supported() was supposed to be pretty much a "const" function > > simply informing whether a given setup is possible. Having it perform > > an actual switch of ops seems to be pushing it... > > dma_supported() is already gone from the public DMA API as it doesn't > make sense to be called separately from set_dma_mask. It will be > entirely gone in the next series after this one. Ah ok, in that case it makes much more sense, we can rename it then. > > What if a driver wants to test various dma masks and then pick one ? > > > > Where does the API documents that if a driver calls dma_supported() it > > then *must* set the corresponding mask and use that ? > > Where is the API document for _any_ of the dma routines? (A: work in > progress by me, but I need to clean up the mess of arch hooks before > it can make any sense) Heh fair enough. > > I don't like a function that is a "boolean query" like this one to have > > such a major side effect. > > > > > From an API standpoint, dma_set_mask() is when the mask is established, > > > > and thus when the ops switch should happen. > > And that's exactly what happens at the driver API level. It just turns > out the dma_capable method is they way better place to actually > implement it, as the ->set_dma_mask method requires lots of code > duplication while not offering any actual benefit over ->dma_capable. > And because of that it's gone after this series. > > In theory we could rename ->dma_capable now, but it would require a > _lot_ of churn. Give me another merge window or two and we should > be down to be about 2 handful of dma_map_ops instance, at which point > we could do all this gratious renaming a lot more easily :) Sure, I get it now, as long as it's not publicly exposed to drivers we are fine. Cheers, Ben.