linux-kernel - Re: [PATCH v7 04/16] drivers: iommu: make of_iommu_set/get

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Date:   Mon, 14 Nov 2016 10:26:54 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Joerg Roedel <joro@...tes.org>, iommu@...ts.linux-foundation.org,
        Will Deacon <will.deacon@....com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Tomasz Nowicki <tn@...ihalf.com>, Jon Masters <jcm@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Sinan Kaya <okaya@...eaurora.org>,
        Nate Watterson <nwatters@...eaurora.org>,
        Prem Mallappa <prem.mallappa@...adcom.com>,
        Dennis Chen <dennis.chen@....com>, linux-acpi@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v7 04/16] drivers: iommu: make of_iommu_set/get_ops() DT
 agnostic

Hi Robin, Joerg,

On Fri, Nov 11, 2016 at 05:43:39PM +0000, Robin Murphy wrote:
> On 11/11/16 16:27, Joerg Roedel wrote:
> > On Fri, Nov 11, 2016 at 04:17:37PM +0000, Robin Murphy wrote:
> >> In the original of_iommu_configure design, the thought was that an ops
> >> structure could be IOMMU-instance-specific (hence the later-removed
> >> "priv" member), so I suppose right now it is mostly a hangover from
> >> that. However, it's also what we initialise a device's fwspec with, so
> >> becomes important again if we're ever going to get past the limitations
> >> of buses-which-are-not-actually-buses[1].
> > 
> > Yeah, I discussed this with a few others at LPC. My current idea is to
> > tell the iommu-core which hardware-iommus exist in the system and a
> > seperate iommu_ops ptr for each of them. Then every struct device can
> > link to the iommu-instance it is translated by.
> 
> Er, that sounds very much like a description of what we already have in
> 4.9-rc. Every struct device now has an iommu_fwspec which encapsulates
> both an iommu_ops pointer (which can perfectly well be per-instance if
> the IOMMU driver wants) and a place for the IOMMU-private data to
> replace the mess of archdata.iommu and driver-internal globals.
> 
> > We are not there yet, but this will give you the same per-device
> > iommu-ops as implemented here.
> 
> With those two patches I linked to, which make the bulk of the IOMMU
> core code per-device-ops-aware off the bat, I'd say we *are* already
> pretty much there. It's only iommu_domain_alloc() which needs a
> device-based alternative, and the non-of_xlate-based IOMMU drivers to
> either call iommu_fwspec_init() for themselves, or perhaps for x86
> plumbing in DMAR/IVRS equivalents of the IORT parsing to the
> infrastructure provided by this series.

I think it all boils down to how we end up implementing the per-device
iommu_ops look-up/binding, question is what do you want me to do with
this patch, it should be fine to drop it and use dev->bus->iommu_ops
for the look-up but I should know sooner rather than later to make
sure the series get another good round of testing.

Please let me know, thank you very much.

Lorenzo