> It shouldn't be a problem to hook something else up to the IOMMU > subsystem. Hopefully it's something that people are going to standardize > on. > > > 3) The automatic attach of DMA domain is also causing a different > > problem for us on the GPU side, preventing us from supporting per- > > context pagetables (since we end up with a disagreement about > > which context bank is used between arm-smmu and the firmware). > > I'm not sure I understand this issue. Is the context bank hard-coded in > the firmware somehow? Or is it possible to rewrite which one is going to > be used at runtime? Do you switch out the actual page tables rather than > the IOMMU domains for context switching? We have a rather long history on this but the tl;dr is that the GPU microcode switches the pagetables by rewriting TTBR0 on the fly (since this is arm-smmu-v2 we have no better option) and yes, unfortunately it is hard coded to use context bank 0. [1] is the current patchset to support all this, including my own take on avoiding the dma-domain (all the cool kids have one). Jordan [1] https://patchwork.freedesktop.org/series/57441/ -- The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
