Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 19 Feb 2020 12:06:28 -0800 | From | isaacm@codeauro ... | Subject | Re: [RFC PATCH] iommu/dma: Allow drivers to reserve an iova range |
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On 2020-02-19 03:15, Will Deacon wrote: > On Tue, Feb 18, 2020 at 05:57:18PM -0800, isaacm@codeaurora.org wrote: >> 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 <lmark@codeaurora.org> >> > > > >> > > > 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? > > Before we dive into designing that, can you please clarify whether the > reserved IOVA range applies to all DMA masters mastering through a > particular SMMU, or whether it's just about one specific master? I was > assuming the former, but wanted to be sure. > This situation currently applies to one master. > Thanks, > > Will
Thanks, Isaac
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