[PATCH v3 02/11] iommu/arm-smmu: Introduce iommu_group notifier block

[Andreas Herrmann]

On Wed, Jan 22, 2014 at 03:33:52PM +0000, Will Deacon wrote:
> On Wed, Jan 22, 2014 at 01:54:11PM +0000, Varun Sethi wrote:
> > > > > Ok, so are you suggesting that we perform the isolation mapping in
> > > > > arm_smmu_add_device and drop the notifier altogether?
> > > > I think that should be fine, until we want to delay mapping creation
> > > > till driver bind time.
> > > 
> > > Is there a hard dependency on that?
> > > 
> > Not sure, may be Andreas can answer that.
> 
> Ok. Andreas? I would have thought doing this *earlier* shouldn't be a
> problem (the DMA ops must be swizzled before the driver is probed).

Yes, I think, there is no hard dependency.

(But still have to double check whether arm_smmu_add_device can be
used instead of the notifier. Will finally see this when doing some
tests.)

> > > > But the "isolate device" property should dictate iommu group creation.
> > > 
> > > The reason we added automatic group creation (per-device) is for VFIO,
> > > which expects all devices to be in a group regardless of the device
> > > isolation configuration.
> > > 
> > IIUC, with the "isolate devices" property we ensure that there would be
> > independent SMR and S2CR per device. Is that correct?
> 
> Yes, as part of giving them independent sets of page tables. Initially these
> tables don't have any valid mappings, but the dma-mapping API will populate
> them in response to dma_map_*/dma_alloc/etc.
> 
> Not sure what this has to do with us putting devices into their own
> groups...
> 
> Will


Andreas