linux-kernel - Re: [PATCH 1/1] iommu/vt-d: Enable PASID during iommu device probe

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Message-ID: <fc1f5412-6041-71b8-2a87-84f2f32456fc@linux.intel.com>
Date:   Fri, 16 Sep 2022 11:05:47 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Ethan Zhao <haifeng.zhao@...ux.intel.com>, iommu@...ts.linux.dev
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Tian <kevin.tian@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] iommu/vt-d: Enable PASID during iommu device probe

On 2022/9/16 10:40, Ethan Zhao wrote:
>>
>> I may not get you exactly. 😄 Some IOMMU features reply on PASID
>> capabilities on both IOMMU and device. The IOMMU drivers enumerate the
>> capabilities and enable them if they are supported.
> I might not express it straightforward,  I mean with this patch iommu 
> deals with
> 
> the complexity of enabling PASID (globally?)  or not at probing stage , 
> instead
> 
> of other device driver side decision to request IOMMU PASID enabling during
> 
> their setup state.  if so you move the decision to iommu probe stage. 
> hmmm...

I am sorry that the commit message was a bit confusing. Actually we
always enable PASID at iommu probe path w/ or w/o this patch.

> 
> Pros,  iommu driver controls everything about PASID enabling.
> 
> Cons,  iommu driver handles all possible complexity about capability 
> matching

Do device drivers need to configure PCI PASID without IOMMU? I searched
the tree and found nothing.

Best regards,
baolu