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

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Date:   Fri, 26 Apr 2019 05:21:15 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Jean-Philippe Brucker <jean-philippe.brucker@....com>
Cc:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Andriy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "christian.koenig@....com" <christian.koenig@....com>
Subject: Re: [PATCH v2 06/19] drivers core: Add I/O ASID allocator

On Fri, Apr 26, 2019 at 12:47:43PM +0100, Jean-Philippe Brucker 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"?
> 
> How about doing the same as CONFIG_IOMMU_IOVA? The code is in
> drivers/iommu but can be selected by non-IOMMU_API users, independently
> of CONFIG_IOMMU_SUPPORT. It's true that this allocator will mostly be
> used by IOMMU drivers.

That is exactly what I meant!