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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 CB345C433E2 for ; Tue, 15 Sep 2020 06:36:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 99FBB2076C for ; Tue, 15 Sep 2020 06:36:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726102AbgIOGg2 (ORCPT ); Tue, 15 Sep 2020 02:36:28 -0400 Received: from verein.lst.de ([213.95.11.211]:46605 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726056AbgIOGgY (ORCPT ); Tue, 15 Sep 2020 02:36:24 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id CFEFC6736F; Tue, 15 Sep 2020 08:36:18 +0200 (CEST) Date: Tue, 15 Sep 2020 08:36:18 +0200 From: Christoph Hellwig To: Matthew Wilcox Cc: Christoph Hellwig , Mauro Carvalho Chehab , Thomas Bogendoerfer , "James E.J. Bottomley" , Joonyoung Shim , Seung-Woo Kim , Ben Skeggs , Marek Szyprowski , Tomasz Figa , Matt Porter , iommu@lists.linux-foundation.org, Stefan Richter , linux1394-devel@lists.sourceforge.net, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linux-samsung-soc@vger.kernel.org, nouveau@lists.freedesktop.org, netdev@vger.kernel.org, linux-scsi@vger.kernel.org, linux-mm@kvack.org, alsa-devel@alsa-project.org Subject: Re: a saner API for allocating DMA addressable pages v2 Message-ID: <20200915063618.GD19113@lst.de> References: <20200914144433.1622958-1-hch@lst.de> <20200914152617.GR6583@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200914152617.GR6583@casper.infradead.org> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Mon, Sep 14, 2020 at 04:26:17PM +0100, Matthew Wilcox wrote: > On Mon, Sep 14, 2020 at 04:44:16PM +0200, Christoph Hellwig wrote: > > I'm still a little unsure about the API naming, as alloc_pages sort of > > implies a struct page return value, but we return a kernel virtual > > address. > > Erm ... dma_alloc_pages() returns a struct page, so is this sentence > stale? Yes. > You say that like it's a bad thing. I think the problem is more that > people don't understand what non-coherent means and think they're > supporting it when they're not. > > dma_alloc_manual_flushing()? That sounds pretty awkward.. > > > As a follow up I plan to move the implementation of the > > DMA_ATTR_NO_KERNEL_MAPPING flag over to this framework as well, given > > that is also is a fundamentally non coherent allocation. The replacement > > for that flag would then return a struct page, as it is allowed to > > actually return pages without a kernel mapping as the name suggested > > (although most of the time they will actually have a kernel mapping..) > > If the page doesn't have a kernel mapping, shouldn't it return a PFN > or a phys_addr? Most APIs we'll feed it into need a struct page. The difference is just that it can be a highmem page. And if we want to get fancy we could change the kernel mapping to PROT_NONE eventually.