From: Rob Herring <firstname.lastname@example.org> To: Mark Kettenis <email@example.com> Cc: firstname.lastname@example.org, Sven Peter <email@example.com>, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: Re: [PATCH 0/3] Apple M1 DART IOMMU driver Date: Tue, 23 Mar 2021 14:53:46 -0600 [thread overview] Message-ID: <20210323205346.GA1283560@robh.at.kernel.org> (raw) In-Reply-To: <firstname.lastname@example.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 <email@example.com> > > > > Hi, > > > > After Hector's initial work  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 . > > 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 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 _______________________________________________ iommu mailing list firstname.lastname@example.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2021-03-23 20:53 UTC|newest] Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-03-20 15:19 Sven Peter via iommu 2021-03-20 15:19 ` [PATCH 1/3] iommu: io-pgtable: add DART pagetable format Sven Peter via iommu 2021-03-24 16:37 ` Robin Murphy 2021-03-25 20:47 ` Sven Peter via iommu 2021-03-20 15:20 ` [PATCH 2/3] dt-bindings: iommu: add DART iommu bindings Sven Peter via iommu 2021-03-22 0:15 ` Rob Herring 2021-03-22 18:16 ` Sven Peter via iommu 2021-03-21 16:00 ` [PATCH 0/3] Apple M1 DART IOMMU driver Mark Kettenis 2021-03-21 17:22 ` Sven Peter via iommu 2021-03-21 18:35 ` Mark Kettenis 2021-03-22 22:17 ` Sven Peter via iommu 2021-03-23 20:00 ` Mark Kettenis 2021-03-23 21:03 ` Sven Peter via iommu 2021-03-21 17:28 ` Sven Peter via iommu 2021-03-23 20:53 ` Rob Herring [this message] 2021-03-23 22:33 ` Mark Kettenis 2021-03-25 7:53 ` Sven Peter via iommu 2021-03-25 11:50 ` Robin Murphy 2021-03-25 20:49 ` Sven Peter via iommu 2021-03-27 15:33 ` Sven Peter via iommu 2021-03-25 21:41 ` Arnd Bergmann 2021-03-26 15:59 ` Mark Kettenis 2021-03-26 16:09 ` Arnd Bergmann 2021-03-26 16:10 ` Sven Peter via iommu 2021-03-26 16:38 ` Arnd Bergmann 2021-03-26 17:06 ` Sven Peter via iommu 2021-03-26 17:26 ` Mark Kettenis 2021-03-26 17:34 ` Robin Murphy 2021-03-26 17:51 ` Sven Peter via iommu 2021-03-26 19:59 ` Arnd Bergmann 2021-03-26 21:16 ` Mark Kettenis 2021-03-27 15:30 ` Sven Peter via iommu 2021-03-26 20:03 ` Arnd Bergmann 2021-03-26 21:13 ` Mark Kettenis 2021-03-24 15:29 ` Robin Murphy 2021-03-25 7:58 ` Sven Peter via iommu
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