Re: [PATCH 2/4] iommu: Add PASID support for DMA mapping API users

[Lu Baolu]

Hi Jacob,

On 12/7/21 9:47 PM, Jacob Pan wrote:
> DMA mapping API is the de facto standard for in-kernel DMA. It operates
> on a per device/RID basis which is not PASID-aware.
>
> Some modern devices such as Intel Data Streaming Accelerator, PASID is
> required for certain work submissions. To allow such devices use DMA
> mapping API, we need the following functionalities:
> 1. Provide device a way to retrieve a kernel PASID for work submission
> 2. Enable the kernel PASID on the IOMMU
> 3. Establish address space for the kernel PASID that matches the default
>     domain. Let it be IOVA or physical address in case of pass-through.
>
> This patch introduces a driver facing API that enables DMA API
> PASID usage. Once enabled, device drivers can continue to use DMA APIs as
> is. There is no difference in dma_handle between without PASID and with
> PASID.

Can a device issue DMA requests with PASID even there's no system IOMMU
or the system IOMMU is disabled?

Best regards,
baolu