[PATCH 18/20] iommu: Add ops->domain_alloc_paging()

[Jason Gunthorpe]

On Thu, May 04, 2023 at 02:35:35PM +0200, Niklas Schnelle wrote:
> On Wed, 2023-05-03 at 16:35 -0300, Jason Gunthorpe wrote:
> > On Wed, May 03, 2023 at 06:17:58PM +0100, Robin Murphy wrote:
> > > On 2023-05-01 19:03, Jason Gunthorpe wrote:
> > > > 
> ---8<---
> > 
> > > > @@ -1940,7 +1944,11 @@ static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
> > > >   	if (type == IOMMU_DOMAIN_IDENTITY && bus->iommu_ops->identity_domain)
> > > >   		return bus->iommu_ops->identity_domain;
> > > > -	domain = bus->iommu_ops->domain_alloc(type);
> > > > +	if ((type == IOMMU_DOMAIN_UNMANAGED || type == IOMMU_DOMAIN_DMA) &&
> > > 
> > > Logically, "type & __IOMMU_DOMAIN_PAGING", otherwise we're already missing
> > > IOMMU_DOMAIN_DMA_FQ. Except maybe that's deliberate? 
> > 
> > It is deliberate for now, if it included FQ it would cause a bunch of
> > ARM64 drivers to switch to lazy mode. I'll add a comment.
> > 
> > I have drafted a followup series that removes all the
> > DMA/DMA_FQ/UNMANAGED checks from the remaining 6 drivers. I did this
> > by adding an op flag 'prefer to use FQ' and made the core code drive
> > the FQ decision from ops.
> 
> Ah that sounds like it could fit very well with s390's need for an even
> lazier flush mode to handle the virtualized IOMMU with slow IOTLB flush
> case aka _SQ / single flush queue mode. When you have anything ready
> give me a ping and I can rework my DMA conversion on top of this.

I'd like to get your S390 dma-api conversion merged ASAP!

I have this general objective to get the modern architectures onto
dma-iommu.c because I want to add new things to the dma-api :\

I had imagined a new op flag because it is is pretty simple, but a
op->get_performance or something that reports some data that could
help dma-iommu.c decide if lazy mode is worthwhile and if there is
other tuning sounds interesting too..

Jason