Cc:     baolu.lu@linux.intel.com, Jacob Pan <jacob.jun.pan@intel.com>,
        Raj Ashok <ashok.raj@intel.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Tony Luck <tony.luck@intel.com>, Yi Liu <yi.l.liu@intel.com>,
        "Tian, Kevin" <kevin.tian@intel.com>,
        Barry Song <21cnbao@gmail.com>,
        "Zanussi, Tom" <tom.zanussi@intel.com>,
        Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH 2/4] iommu: Add PASID support for DMA mapping API users
To:     Jacob Pan <jacob.jun.pan@linux.intel.com>,
        iommu@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Christoph Hellwig <hch@infradead.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.com>
References: <1638884834-83028-1-git-send-email-jacob.jun.pan@linux.intel.com>
 <1638884834-83028-3-git-send-email-jacob.jun.pan@linux.intel.com>
From:   Lu Baolu <baolu.lu@linux.intel.com>
Message-ID: <16408193-c8bc-3046-b32f-9274bf0b415c@linux.intel.com>
Date:   Wed, 8 Dec 2021 10:31:36 +0800
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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