RE: [RFC/PATCH 2/7] iommu-api: Add map_range/unmap_range functions

[Varun Sethi <Varun.Sethi@freescale.com>]

> -----Original Message-----
> From: iommu-bounces@lists.linux-foundation.org [mailto:iommu-
> bounces@lists.linux-foundation.org] On Behalf Of Will Deacon
> Sent: Tuesday, July 01, 2014 3:04 PM
> To: Olav Haugan
> Cc: linux-arm-msm@vger.kernel.org; iommu@lists.linux-foundation.org;
> thierry.reding@gmail.com; vgandhi@codeaurora.org; linux-arm-
> kernel@lists.infradead.org
> Subject: Re: [RFC/PATCH 2/7] iommu-api: Add map_range/unmap_range
> functions
> 
> Hi Olav,
> 
> On Mon, Jun 30, 2014 at 05:51:51PM +0100, Olav Haugan wrote:
> > Mapping and unmapping are more often than not in the critical path.
> > map_range and unmap_range allows SMMU driver implementations to
> > optimize the process of mapping and unmapping buffers into the SMMU
> page tables.
> > Instead of mapping one physical address, do TLB operation (expensive),
> > mapping, do TLB operation, mapping, do TLB operation the driver can
> > map a scatter-gatherlist of physically contiguous pages into one
> > virtual address space and then at the end do one TLB operation.
> >
> > Additionally, the mapping operation would be faster in general since
> > clients does not have to keep calling map API over and over again for
> > each physically contiguous chunk of memory that needs to be mapped to
> > a virtually contiguous region.
> 
> I like the idea of this, although it does mean that drivers implementing
> the range mapping functions need more featureful page-table manipulation
> code than currently required.
> 
> For example, iommu_map uses iommu_pgsize to guarantee that mappings are
> created in blocks of the largest support page size. This can be used to
> simplify iterating in the SMMU driver (although the ARM SMMU driver
> doesn't yet make use of this, I think Varun would add this when he adds
> support for sections).
Yes, this would be supported.

-Varun