Re: [PATCH v3 10/20] iommu: Add set_platform_dma iommu ops

[Jason Gunthorpe]

On Mon, Nov 28, 2022 at 02:46:38PM +0800, Lu Baolu wrote:
> When VFIO finishes assigning a device to user space and calls
> iommu_group_release_dma_owner() to return the device to kernel, the IOMMU
> core will attach the default domain to the device. Unfortunately, some
> IOMMU drivers don't support default domain, hence in the end, the core
> calls .detach_dev instead.
> 
> This adds set_platform_dma iommu ops to make it clear that what it does
> is returning control back to the platform DMA ops.
> 
> Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  include/linux/iommu.h | 4 ++++
>  1 file changed, 4 insertions(+)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

> + * @set_platform_dma: Returning control back to the platform DMA ops. Only
> + *                    valid for IOMMU drivers which don't support default
> + *                    domain.

I would add:

  This op is to support old IOMMU drivers, new drivers should use
  default domains, and the common IOMMU DMA ops.

Jason