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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-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210323_205349_749253_927896AB X-CRM114-Status: GOOD ( 50.42 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel