linux-kernel - Re: [PATCH 0/7] iommu: Permit modular builds of ARM SMMU[v3] drivers

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Message-ID: <20191101172145.GA3983@willie-the-truck>
Date:   Fri, 1 Nov 2019 17:21:46 +0000
From:   Will Deacon <will@...nel.org>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     Saravana Kannan <saravanak@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 0/7] iommu: Permit modular builds of ARM SMMU[v3] drivers

Hi Jean-Philippe,

Quick question while you figure out the devlink stuff with Saravana...

On Thu, Oct 31, 2019 at 08:37:58PM +0100, Jean-Philippe Brucker wrote:
> On Wed, Oct 30, 2019 at 05:57:44PM -0700, Saravana Kannan via iommu wrote:
> > > > > Obviously you need to be careful about using IOMMU drivers as modules,
> > > > > since late loading of the driver for an IOMMU serving active DMA masters
> > > > > is going to end badly in many cases. On Android, we're using device links
> > > > > to ensure that the IOMMU probes first.
> > > >
> > > > Out of curiosity, which device links are those? Clearly not the RPM links
> > > > created by the IOMMU drivers themselves... Is this some special Android
> > > > magic, or is there actually a chance of replacing all the
> > > > of_iommu_configure() machinery with something more generic?
> > >
> > > I'll admit that I haven't used them personally yet, but I'm referring to
> > > this series from Saravana [CC'd]:
> > >
> > > https://lore.kernel.org/linux-acpi/20190904211126.47518-1-saravanak@google.com/
> > >
> > > which is currently sitting in linux-next now that we're upstreaming the
> > > "special Android magic" ;)
> 
> Neat, I'm trying to do the same for virtio-iommu. It needs to be modular
> because it depends on the virtio transport, which distributions usually
> build as a module. So far I've been managing the device links in
> virtio-iommu's add_device() and remove_device() callbacks [1]. Since it
> relies on the existing probe deferral, I had to make a special case for
> virtio-iommu to avoid giving up after initcalls_done [2].

As far as symbols exported from the IOMMU and PCI layers, did you find you
needed anything on top of the stuff I'm exporting in patches 1 and 3?

Cheers,

Will