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,DKIM_SIGNED, DKIM_VALID,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 E4862C43461 for ; Tue, 15 Sep 2020 06:37:24 +0000 (UTC) Received: from alsa0.perex.cz (alsa0.perex.cz [77.48.224.243]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id E99D02076C for ; Tue, 15 Sep 2020 06:37:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alsa-project.org header.i=@alsa-project.org header.b="Tb1A0X9q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E99D02076C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=alsa-devel-bounces@alsa-project.org Received: from alsa1.perex.cz (alsa1.perex.cz [207.180.221.201]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa0.perex.cz (Postfix) with ESMTPS id 6C0971663; Tue, 15 Sep 2020 08:36:32 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa0.perex.cz 6C0971663 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=alsa-project.org; s=default; t=1600151842; bh=J5/pXeI6U7hyoZtAFY/YjKsWVVrZ0oM4sEqSQ8AcGHM=; h=Date:From:To:Subject:References:In-Reply-To:Cc:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From; b=Tb1A0X9qXviLuz+t6kRlH7aZPJIietU5Y51CW32DyXZontfQ47sXPWBGPCvVd/5Vq zT5iXXAwBsklrBPrcVB7+BmmyTT1nietbB/irSoY428v8qGjV+6XGwxccKBEGuC/yp y5+jGPOYFmUqI3G7oEZkV5iZ3u9oEhmFA9VdE6Fk= Received: from alsa1.perex.cz (localhost.localdomain [127.0.0.1]) by alsa1.perex.cz (Postfix) with ESMTP id E2947F80212; Tue, 15 Sep 2020 08:36:31 +0200 (CEST) Received: by alsa1.perex.cz (Postfix, from userid 50401) id 61FC8F80212; Tue, 15 Sep 2020 08:36:26 +0200 (CEST) Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa1.perex.cz (Postfix) with ESMTPS id 2C88BF80146 for ; Tue, 15 Sep 2020 08:36:20 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz 2C88BF80146 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 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) Cc: alsa-devel@alsa-project.org, linux-doc@vger.kernel.org, nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org, "James E.J. Bottomley" , linux-mm@kvack.org, linux1394-devel@lists.sourceforge.net, Christoph Hellwig , Marek Szyprowski , linux-samsung-soc@vger.kernel.org, Joonyoung Shim , linux-scsi@vger.kernel.org, Ben Skeggs , Matt Porter , linux-media@vger.kernel.org, Mauro Carvalho Chehab , linux-arm-kernel@lists.infradead.org, Thomas Bogendoerfer , linux-parisc@vger.kernel.org, netdev@vger.kernel.org, Seung-Woo Kim , linux-mips@vger.kernel.org, Tomasz Figa , iommu@lists.linux-foundation.org, Stefan Richter X-BeenThere: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" 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.