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Date: Thu, 13 Feb 2020 17:23:23 +0000 From: Robin Murphy <robin.murphy@....com> To: Thierry Reding <thierry.reding@...il.com>, Arnd Bergmann <arnd@...db.de>, Will Deacon <will@...nel.org>, Rob Herring <robh+dt@...nel.org> Cc: Joerg Roedel <joro@...tes.org>, Olof Johansson <olof@...om.net>, linux-tegra@...r.kernel.org, iommu@...ts.linux-foundation.org, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, Maxime Ripard <mripard@...nel.org> Subject: Re: [PATCH v4 0/5] memory: Introduce memory controller mini-framework [+ Maxime] On 13/02/2020 4:39 pm, Thierry Reding wrote: > From: Thierry Reding <treding@...dia.com> > > Hi, > > this set of patches adds a new binding that allows device tree nodes to > explicitly define the DMA parent for a given device. This supplements > the existing interconnect bindings and is useful to disambiguate in the > case where a device has multiple paths to system memory. Beyond that it > can also be useful when there aren't any actual interconnect paths that > can be controlled, so in simple cases this can serve as a simpler > variant of interconnect paths. Isn't that still squarely the intent of the "dma-mem" binding, though? i.e. it's not meant to be a 'real' interconnect provider, but a very simple way to encode DMA parentage piggybacked onto a more general binding (with the *option* of being a full-blown interconnect if it wants to, but certainly no expectation). Robin. > One other case where this is useful is to describe the relationship > between devices such as the memory controller and an IOMMU, for example. > On Tegra186 and later, the memory controller is programmed with a set of > stream IDs that are to be associated with each memory client. This > programming needs to happen before translations through the IOMMU start, > otherwise the used stream IDs may deviate from the expected values. The > memory-controllers property is used in this case to ensure that the > memory controller driver has been probed (and hence has programmed the > stream ID mappings) before the IOMMU becomes available. > > Patch 1 introduces the memory controller bindings, both from the > perspective of the provider and the consumer. Patch 2 makes use of a > memory-controllers property to determine the DMA parent for the purpose > of setting up DMA masks (based on the dma-ranges property of the DMA > parent). Patch 3 introduces a minimalistic framework that is used to > register memory controllers with along with a set of helpers to look up > the memory controller from device tree. > > An example of how to register a memory controller is shown in patch 4 > for Tegra186 (and later) and finally the ARM SMMU driver is extended to > become a consumer of an (optional) memory controller. As described > above, the goal is to defer probe as long as the memory controller has > not yet programmed the stream ID mappings. > > Thierry > > Thierry Reding (5): > dt-bindings: Add memory controller bindings > of: Use memory-controllers property for DMA parent > memory: Introduce memory controller mini-framework > memory: tegra186: Register as memory controller > iommu: arm-smmu: Get reference to memory controller > > .../bindings/memory-controllers/consumer.yaml | 14 + > .../memory-controllers/memory-controller.yaml | 32 +++ > drivers/iommu/arm-smmu.c | 11 + > drivers/iommu/arm-smmu.h | 2 + > drivers/memory/Makefile | 1 + > drivers/memory/core.c | 248 ++++++++++++++++++ > drivers/memory/tegra/tegra186.c | 9 +- > drivers/of/address.c | 25 +- > include/linux/memory-controller.h | 34 +++ > 9 files changed, 366 insertions(+), 10 deletions(-) > create mode 100644 Documentation/devicetree/bindings/memory-controllers/consumer.yaml > create mode 100644 Documentation/devicetree/bindings/memory-controllers/memory-controller.yaml > create mode 100644 drivers/memory/core.c > create mode 100644 include/linux/memory-controller.h >
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