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

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Date:   Fri, 11 Nov 2016 17:43:39 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        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

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.

Robin.