[Freedreno] [PATCH RESEND 0/7] iommu: Permit modular builds of io-pgtable drivers

[Will Deacon]

On Mon, Jan 04, 2021 at 11:36:38PM -0800, Isaac J. Manjarres wrote:
> The goal of the Generic Kernel Image (GKI) effort is to have a common
> kernel image that works across multiple Android devices. This involves
> generating a kernel image that has core features integrated into it,
> while SoC specific functionality can be added to the kernel for the
> device as a module.
> 
> Along with modularizing IOMMU drivers, this also means building the
> io-pgtable code as modules, which allows for SoC vendors to only include
> the io-pgtable implementations that they use. For example, GKI for arm64
> must include support for both the IOMMU ARM LPAE/V7S formats at the
> moment. Having the code for both formats as modules allows SoC vendors
> to only provide the page table format that they use, along with their
> IOMMU driver.

Why is this desirable for upstream? This code isn't especially large, and
the formats we support are largely architectural, meaning that they are
shared between different IOMMU drivers. I think that making this modular
just means that out-of-tree modifications are likely to generate page-tables
which are specific to a particular IOMMU, and lead to horrible problems
(crashes and data corruption) if another IOMMU driver tries to use them.

Please can you upstream whatever changes you want to make instead?

Will