On Mon, Apr 30, 2018 at 12:41:52PM +0100, Robin Murphy wrote: > On 30/04/18 12:02, Thierry Reding wrote: > > On Thu, Apr 26, 2018 at 02:11:36PM +0200, Thierry Reding wrote: > > > On Wed, Apr 25, 2018 at 08:19:34AM -0700, Christoph Hellwig wrote: > > > > On Wed, Apr 25, 2018 at 12:10:48PM +0200, Thierry Reding wrote: > > > > > From: Thierry Reding <treding@xxxxxxxxxx> > > > > > > > > > > The dma_iommu_detach_device() API can be used by drivers to forcibly > > > > > detach a device from an IOMMU that architecture code might have attached > > > > > to. This is useful for drivers that need explicit control over the IOMMU > > > > > using the IOMMU API directly. > > > > > > > > Given that no one else implements it making it a generic API seems > > > > rather confusing. For now I'd rename it to > > > > arm_dma_iommu_detach_device() and only implement it in arm. > > > > > > That'd be suboptimal because this code is used on both 32-bit and 64-bit > > > ARM. If we make the function 32-bit ARM specific then the driver code > > > would need to use an #ifdef to make sure compilation doesn't break on > > > 64-bit ARM. > > > > Do you still want me to make this ARM specific? While I haven't > > encountered this issue on 64-bit ARM yet, I think it would happen there > > as well, under the right circumstances. I could take a shot at > > implementing the equivalent there (which means essentially implementing > > it for drivers/iommu/dma-iommu.c and calling that from 64-bit ARM code). > > It sounds like things are getting a bit backwards here: iommu-dma should > have nothing to do with this, since if you've explicitly attached the device > to your own IOMMU domain then you're already bypassing everything it knows > about and has control over. Arch code calling into iommu-dma to do something > which makes arch code not use iommu-dma makes very little sense. My understanding is that iommu-dma will set up an IOMMU domain at device probe time anyway. So even if attaching to an own IOMMU domain will end up bypassing iommu-dma, we'd still want to clear up the IOMMU domain and any associated resources, right? Thierry
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