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=-4.0 required=3.0 tests=BAYES_00,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 D7924C433C1 for ; Tue, 23 Mar 2021 20:54:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AE9D9619D2 for ; Tue, 23 Mar 2021 20:54:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233378AbhCWUyS (ORCPT ); Tue, 23 Mar 2021 16:54:18 -0400 Received: from mail-il1-f179.google.com ([209.85.166.179]:40952 "EHLO mail-il1-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233355AbhCWUxt (ORCPT ); Tue, 23 Mar 2021 16:53:49 -0400 Received: by mail-il1-f179.google.com with SMTP id c17so19436046ilj.7; Tue, 23 Mar 2021 13:53:48 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=PHYJdMOhlozVGJVh1oALPNAZWOy/E29w1l72RoruR20=; b=CV8TSCJq2YlNT9JAfKtdKNhSacBv30XWeTy3yQuQHzXH+CcqEaQqSkKxfb+Y/3ukdz PBlSUrY2dzZ5m/3C+WJxG4DR7toLNm5Pl5RdZShcatXpySyysKGtgZkBGVNprQsJSiDX HCVjNyRDddXGcahqwR+FVLDg9O4R2gl1G3QKLK/s4A3R2qbVtgLmji0gb9PfolYHhMU7 WWpAuICDBytfnzXyBQCoI7XnJ2vDJgODWwmUlZ0WvFJaxpIB6GS3ga8bk+r10dtlpWMy 4yEYEC8SaTDJSfdcvhRJlIgw7Re4NmRrnmAyP2S5+7w3i08NIiIjrMFEmIL+YhhukH54 VOgg== X-Gm-Message-State: AOAM5309EFtyp0fjpKQcz7vVSRruoO5WYCgXp3inwTYQyL9AWbKDO1CL Pi9H3YQldNoLQyE/kSSC0w== X-Google-Smtp-Source: ABdhPJwAkhqmMD7d8QqODSssQ97V2pFypdhqwqehElXuGTHngBGyJOmgjnNRf8y1zQyPvSz1qRMvEA== X-Received: by 2002:a05:6e02:158c:: with SMTP id m12mr75161ilu.121.1616532828308; Tue, 23 Mar 2021 13:53:48 -0700 (PDT) Received: from robh.at.kernel.org ([64.188.179.253]) by smtp.gmail.com with ESMTPSA id d3sm11345ilo.32.2021.03.23.13.53.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Mar 2021 13:53:47 -0700 (PDT) Received: (nullmailer pid 1302881 invoked by uid 1000); Tue, 23 Mar 2021 20:53:46 -0000 Date: Tue, 23 Mar 2021 14:53:46 -0600 From: Rob Herring To: Mark Kettenis Cc: Sven Peter , iommu@lists.linux-foundation.org, joro@8bytes.org, will@kernel.org, robin.murphy@arm.com, arnd@kernel.org, marcan@marcan.st, maz@kernel.org, mohamed.mediouni@caramail.com, stan@corellium.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org Subject: Re: [PATCH 0/3] Apple M1 DART IOMMU driver Message-ID: <20210323205346.GA1283560@robh.at.kernel.org> References: <20210320151903.60759-1-sven@svenpeter.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Sun, Mar 21, 2021 at 05:00:50PM +0100, Mark Kettenis wrote: > > Date: Sat, 20 Mar 2021 15:19:33 +0000 > > From: Sven Peter > > > > Hi, > > > > After Hector's initial work [1] to bring up Linux on Apple's M1 it's time to > > bring up more devices. Most peripherals connected to the SoC are behind a iommu > > which Apple calls "Device Address Resolution Table", or DART for short [2]. > > Unfortunately, it only shares the name with PowerPC's DART. > > Configuring this iommu is mandatory if these peripherals require DMA access. > > > > This patchset implements initial support for this iommu. The hardware itself > > uses a pagetable format that's very similar to the one already implement in > > io-pgtable.c. There are some minor modifications, namely some details of the > > PTE format and that there are always three pagetable levels, which I've > > implement as a new format variant. > > > > I have mainly tested this with the USB controller in device mode which is > > compatible with Linux's dwc3 driver. Some custom PHY initialization (which is > > not yet ready or fully understood) is required though to bring up the ports, > > see e.g. my patches to our m1n1 bootloader [3,4]. If you want to test the same > > setup you will probably need that branch for now and add the nodes from > > the DT binding specification example to your device tree. > > > > Even though each DART instances could support up to 16 devices usually only > > a single device is actually connected. Different devices generally just use > > an entirely separate DART instance with a seperate MMIO range, IRQ, etc. > > > > I have just noticed today though that at least the USB DWC3 controller in host > > mode uses *two* darts at the same time. I'm not sure yet which parts seem to > > require which DART instance. > > > > This means that we might need to support devices attached to two iommus > > simultaneously and just create the same iova mappings. Currently this only > > seems to be required for USB according to Apple's Device Tree. > > > > I see two options for this and would like to get feedback before > > I implement either one: > > > > 1) Change #iommu-cells = <1>; to #iommu-cells = <2>; and use the first cell > > to identify the DART and the second one to identify the master. > > The DART DT node would then also take two register ranges that would > > correspond to the two DARTs. Both instances use the same IRQ and the > > same clocks according to Apple's device tree and my experiments. > > This would keep a single device node and the DART driver would then > > simply map iovas in both DARTs if required. > > > > 2) Keep #iommu-cells as-is but support > > iommus = <&usb_dart1a 1>, <&usb_dart1b 0>; > > instead. > > This would then require two devices nodes for the two DART instances and > > some housekeeping in the DART driver to support mapping iovas in both > > DARTs. > > I believe omap-iommu.c supports this setup but I will have to read > > more code to understand the details there and figure out how to implement > > this in a sane way. > > > > I currently prefer the first option but I don't understand enough details of > > the iommu system to actually make an informed decision. Please don't mix what does the h/w look like and what's easy to implement in Linux's IOMMU subsytem. It's pretty clear (at least from the description here) that option 2 reflects the h/w. > > I'm obviously also open to more options :-) > > Hi Sven, > > I don't think the first option is going to work for PCIe. PCIe > devices will have to use "iommu-map" properties to map PCI devices to > the right iommu, and the currently implementation seems to assume that > #iommu-cells = <1>. The devictree binding[1] doesn't explicitly state > that it relies on #iommu-cells = <1>, but it isn't clear how the > rid-base to iommu-base mapping mechanism would work when that isn't > the case. > > Now the PCIe DARTs are simpler and seem to have only one "instance" > per DART. So if we keep #iommu-cells = <1> for those, you'd still be > fine using the first approach. > > As I mentioned before, not all DARTs support the full 32-bit aperture. > In particular the PCIe DARTs support a smaller address-space. It is > not clear whether this is a restriction of the PCIe host controller or > the DART, but the Apple Device Tree has "vm-base" and "vm-size" > properties that encode the base address and size of the aperture. > These single-cell properties which is probably why for the USB DARTs > only "vm-base" is given; since "vm-base" is 0, a 32-bit number > wouldn't be able to encode the full aperture size. We could make them > 64-bit numbers in the Linux device tree though and always be explicit > about the size. Older Sun SPARC machines used a single "virtual-dma" > property to encode the aperture. We could do someting similar. You > would use this property to initialize domain->geometry.aperture_start > and domain->geometry.aperture_end in diff 3/3 of this series. 'dma-ranges' is what should be used here. Rob