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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 089E8C43461 for ; Mon, 14 Sep 2020 15:26:52 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 82BD320665 for ; Mon, 14 Sep 2020 15:26:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="M80c+D3B" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 82BD320665 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id AC95C900007; Mon, 14 Sep 2020 11:26:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A77AA900003; Mon, 14 Sep 2020 11:26:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 966AE900007; Mon, 14 Sep 2020 11:26:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0101.hostedemail.com [216.40.44.101]) by kanga.kvack.org (Postfix) with ESMTP id 7EE76900003 for ; Mon, 14 Sep 2020 11:26:50 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 2FE57181AC9CB for ; Mon, 14 Sep 2020 15:26:50 +0000 (UTC) X-FDA: 77262044580.28.ducks52_020773627109 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin28.hostedemail.com (Postfix) with ESMTP id E104F6C04 for ; Mon, 14 Sep 2020 15:26:49 +0000 (UTC) X-HE-Tag: ducks52_020773627109 X-Filterd-Recvd-Size: 3689 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf22.hostedemail.com (Postfix) with ESMTP for ; Mon, 14 Sep 2020 15:26:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=7O2Rc307Jq8KkaDn7zbVItvtt/ecHc/too3yP9zxMNw=; b=M80c+D3BqJySppi+H3eNYCcnH/ gkfi1LX5tkOxqiYr7vGlDhimfScWmyFoD4H7IZc29yxj59fxiZw4CTf73qE/Frs6kv2D1VP9Z0cDk mxHwC6y23VXZp0GWVeuCJj/TuYsYfRbshYeLxTfn4NkxNbZt/mCYZDG48aAzhZnPSD26Tjx+8/mwu 2BX9yzKsoQKr11uV/Bwnigc9od3UdV8s2rG69+T+l2QU+9l3XPVzWYgBbLqR3TeV+3H8nv+hHYZRQ AbZDHlAxP767K2OWIVLYATsG32mlziFsc93sPs4pmGxH1oa7RFwa/hq19KGZWcLA7yuKXtQ9v35Ul oAwe3FdQ==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kHqN0-0004bK-27; Mon, 14 Sep 2020 15:26:18 +0000 Date: Mon, 14 Sep 2020 16:26:17 +0100 From: Matthew Wilcox To: Christoph Hellwig Cc: 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: <20200914152617.GR6583@casper.infradead.org> References: <20200914144433.1622958-1-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200914144433.1622958-1-hch@lst.de> X-Rspamd-Queue-Id: E104F6C04 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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? >From patch 14: +struct page *dma_alloc_pages(struct device *dev, size_t size, + dma_addr_t *dma_handle, enum dma_data_direction dir, gfp_t gfp); > The other alternative would be to name the API > dma_alloc_noncoherent, but the whole non-coherent naming seems to put > people off. 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()? > 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?