Re: [PATCH 0/9] Renesas ipmmu-vmsa: Miscellaneous cleanups and fixes

[Will Deacon <will.deacon@arm.com>]

On Mon, Apr 21, 2014 at 03:13:00PM +0100, Laurent Pinchart wrote:
> Hello,

Hi Laurent,

> This patch set cleans up and fixes small issues in the ipmmu-vmsa driver. The
> patches are based on top of "[PATCH v3] iommu: Add driver for Renesas
> VMSA-compatible IPMMU" that adds the ipmmu-vmsa driver.
> 
> The most interesting part of this series is the rewrite of the page table
> management code. The IOMMU core guarantees that the map and unmap operations
> will always be called only with page sizes advertised by the driver. We can
> use that assumption to remove loops of PGD and PMD entries, simplifying the
> code.

Hmm, interesting. We still have to handle the case where a mapping created
with one page-size could be unmapped with another though (in particular,
unmapping part of the range).

> Will, would it make sense to perform the same cleanup for the arm-smmu driver,
> or is there a reason to keep loops over PGD and PMD entries ? Removing them
> makes the implementation of 68kB and 2MB pages easier.

Is this an assumption that's relied on by other IOMMU drivers? It
certainly makes mapping of large ranges less efficient than it could be, so
I'm more inclined to set all the bits > PAGE_SIZE in pgsize_bitmap if it's
only used to determine the granularity at which map/unmap are called (which
is unrelated to what the hardware can actually do).

Will