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=-0.5 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 31668C34031 for ; Wed, 19 Feb 2020 01:57:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0275F24654 for ; Wed, 19 Feb 2020 01:57:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="key not found in DNS" (0-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="jCnEFdP9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728063AbgBSB5W (ORCPT ); Tue, 18 Feb 2020 20:57:22 -0500 Received: from mail26.static.mailgun.info ([104.130.122.26]:51246 "EHLO mail26.static.mailgun.info" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727811AbgBSB5V (ORCPT ); Tue, 18 Feb 2020 20:57:21 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1582077441; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=YcNZbJFJfQvxvpBXUgrKzCwdLhDCfSRbsPpwRd/fJ3g=; b=jCnEFdP9VI5UbkPRAPAoCa7Xw0z9kJmiB40Unaz7Yaa65rO0OLbLYQBsKr1uJdFlflmBMTkn I5D8qPW3ybwpbLiqRIoFNCK7rJYM9s7bivL8CjIHDCfRSKmI+juQSKwZe6jMn4g8aEOALVQv ezjvyYchuV9yW+lz3RhLEeOtHZo= X-Mailgun-Sending-Ip: 104.130.122.26 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by mxa.mailgun.org with ESMTP id 5e4c9600.7f24b588bf80-smtp-out-n02; Wed, 19 Feb 2020 01:57:20 -0000 (UTC) Received: by smtp.codeaurora.org (Postfix, from userid 1001) id E5C36C4479D; Wed, 19 Feb 2020 01:57:19 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: isaacm) by smtp.codeaurora.org (Postfix) with ESMTPSA id E6337C43383; Wed, 19 Feb 2020 01:57:18 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 18 Feb 2020 17:57:18 -0800 From: isaacm@codeaurora.org To: Robin Murphy Cc: Christoph Hellwig , pratikp@codeaurora.org, linux-kernel@vger.kernel.org, Liam Mark , iommu@lists.linux-foundation.org, kernel-team@android.com Subject: Re: [RFC PATCH] iommu/dma: Allow drivers to reserve an iova range In-Reply-To: References: <1581721096-16235-1-git-send-email-isaacm@codeaurora.org> <20200217080138.GB10342@infradead.org> Message-ID: X-Sender: isaacm@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-02-17 07:50, Robin Murphy wrote: > On 17/02/2020 8:01 am, Christoph Hellwig wrote: >> On Fri, Feb 14, 2020 at 02:58:16PM -0800, Isaac J. Manjarres wrote: >>> From: Liam Mark >>> >>> Some devices have a memory map which contains gaps or holes. >>> In order for the device to have as much IOVA space as possible, >>> allow its driver to inform the DMA-IOMMU layer that it should >>> not allocate addresses from these holes. >> >> Layering violation. dma-iommu is the translation layer between the >> DMA API and the IOMMU API. And calls into it from drivers performing >> DMA mappings need to go through the DMA API (and be documented there). > > +1 > > More than that, though, we already have "holes in the address space" > support for the sake of PCI host bridge windows - assuming this is the > same kind of thing (i.e. the holes are between memory regions and > other resources in PA space, so are only relevant once address > translation comes into the picture), then this is IOMMU API level To make sure that we're on the same page, this support alludes to the handling in dma-iommu.c that reserves portions of the IOVA space for the PCI host bridge windows, correct? If so, then yes, this is similar. > stuff, so even a DMA API level interface would be inappropriate. Does this mean that the driver should be managing the IOVA space and mappings for this device using the IOMMU API? If so, is the rationale for this because the device driver can have the information of what IOVA ranges can and cannot be used? Shouldn't there be a generic way of informing an IOMMU driver about these reserved ranges? Perhaps through a device tree property, instead of deferring this type of management to the driver? > > Robin.