Re: [PATCH v2] iommu/arm: Add module parameter to set msi iova address

[Will Deacon]

On Mon, Sep 14, 2020 at 11:13:07AM -0700, Vennila Megavannan wrote:
> From: Srinath Mannam <srinath.mannam@xxxxxxxxxxxx>
> 
> Add provision to change default value of MSI IOVA base to platform's
> suitable IOVA using module parameter. The present hardcoded MSI IOVA base
> may not be the accessible IOVA ranges of platform.
> 
> If any platform has the limitaion to access default MSI IOVA, then it can
> be changed using "arm-smmu.msi_iova_base=0xa0000000" command line argument.
> 
> Signed-off-by: Srinath Mannam <srinath.mannam@xxxxxxxxxxxx>
> Co-developed-by: Vennila Megavannan <vemegava@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Vennila Megavannan <vemegava@xxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 5 ++++-
>  drivers/iommu/arm/arm-smmu/arm-smmu.c       | 5 ++++-
>  2 files changed, 8 insertions(+), 2 deletions(-)

This feels pretty fragile. Wouldn't it be better to realise that there's
a region conflict with iommu_dma_get_resv_regions() and move the MSI window
accordingly at runtime?

Will