linux-kernel - Re: [PATCH v2 06/19] drivers core: Add I/O ASID allocator

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Message-ID: <20190425111912.0e15eb7d@jacob-builder>
Date:   Thu, 25 Apr 2019 11:19:12 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Eric Auger <eric.auger@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Andriy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v2 06/19] drivers core: Add I/O ASID allocator

Hi Christoph,

On Tue, 23 Apr 2019 23:19:03 -0700
Christoph Hellwig <hch@...radead.org> wrote:

> On Tue, Apr 23, 2019 at 04:31:06PM -0700, Jacob Pan wrote:
> > The allocator doesn't really belong in drivers/iommu because some
> > drivers would like to allocate PASIDs for devices that aren't
> > managed by an IOMMU, using the same ID space as IOMMU. It doesn't
> > really belong in drivers/pci either since platform device also
> > support PASID. Add the allocator in drivers/base.  
> 
> I'd still add it to drivers/iommu, just selectable separately from the
> core iommu code..
Perhaps I misunderstood. If a driver wants to use IOASIDs w/o iommu
subsystem even turned on, how could selecting from the core iommu code
help? Could you elaborate on "selectable"?

>From VT-d's perspective, PASIDs are only used with IOMMU on. Jean
knows other use cases.

Jacob