On Thu, Feb 02, 2017 at 09:15:19PM +0530, Sricharan wrote: > Hi Rob, > > >-----Original Message----- > >From: linux-arm-kernel [mailto:linux-arm-kernel-boun...@lists.infradead.org] > >On Behalf Of Rob Clark > >Sent: Thursday, February 02, 2017 8:33 PM > >To: Joerg Roedel <j...@8bytes.org> > >Cc: Will Deacon <will.dea...@arm.com>; iommu@lists.linux-foundation.org; > >Sricharan <sricha...@codeaurora.org>; linux-arm- > >ker...@lists.infradead.org > >Subject: Re: [PATCH 0/5] Implement SMMU passthrough using the default domain > > > >On Thu, Jan 26, 2017 at 12:18 PM, Joerg Roedel <j...@8bytes.org> wrote: > >> On Tue, Jan 24, 2017 at 08:42:23PM +0530, Sricharan wrote: > >>> Thanks for this series. We had a case with the GPU. > >>> The GPU's iommu was setup by kernel and the GPU > >>> also does dynamic updates for on-the-fly switching between > >>> process pagetables. GPU driver was not using DMA domain and > >>> the GPU's firmware was always expecting to run out of contextbank > >>> '0' (although not correct) , which was not the case after the DMA domain > >>> was made default as '0' was getting allocated for DMA domain and > >>> there were concerns about reusing the DMA domain as well. > >>> Now with this series, looks there is an way out of that that can be tried. > >>> > >>> So should the default domain not be per device specific selectable ? > >> > >> Note that iommu-drivers can request direct-mapping for any given device > >> on its initializtion. This is used on x86 for devices that need a 1-1 > >> mapping for some reason. > >> > >> Also device drivers can use the iommu-api and assign their own domain to > >> a device, which allows them to manage the dma address space on their > >> own. > > > >Part of the problem is that dev->archdata.dma_ops gets wired up to > >iommu_dma_ops. Which isn't so bad on it's own, except that cache ops > >are not exposed to drivers, forcing us to use dma-mapping API > >(dma_map_sg, etc) for cache operations. > > > >Possibly we should just expose cache op's to drivers bypass this abuse > >of dma-mapping. > > > [1], with this, when the default domain in not DOMAIN_DMA, then > dev->archdata.dma_ops is not set to iommu_dma_ops , instead remains > to be swiotlb_ops. Is that not correct for gpu's unmanaged domain case ? > > https://www.spinics.net/lists/arm-kernel/msg556209.html > > >btw, Will, we definitely want this to *not* rely on kcmdline for the > >gpu with it's own private iommu case.. > > Ya, that changes behavior for all devices and some might want > DMA_DOMAIN and some UNMANAGED.
My patch changes the *default* domain. When would this ever be UNMANAGED? If you're using an UNMANAGED domain, I think you need to take care of the DMA ops yourself. There are likely missing functions to do that, but they should be added in a separate series. Will _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
