linux-kernel - Re: [PATCH v2 1/2] iommu: add support for drivers that manage iommu explicitly

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Message-ID: <CAF6AEGsFmuO5M_RWm-RjDT_F_1Z=MLYmNqRXqFNDR7aUoPaMdg@mail.gmail.com>
Date:   Tue, 10 Sep 2019 08:34:13 -0700
From:   Rob Clark <robdclark@...il.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>,
        Rob Clark <robdclark@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Sudeep Holla <sudeep.holla@....com>,
        Joe Perches <joe@...ches.com>, Arnd Bergmann <arnd@...db.de>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] iommu: add support for drivers that manage iommu explicitly

On Tue, Sep 10, 2019 at 1:14 AM Joerg Roedel <joro@...tes.org> wrote:
>
> On Fri, Sep 06, 2019 at 02:44:01PM -0700, Rob Clark wrote:
> > @@ -674,7 +674,7 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)
> >
> >       mutex_lock(&group->mutex);
> >       list_add_tail(&device->list, &group->devices);
> > -     if (group->domain)
> > +     if (group->domain && !(dev->driver && dev->driver->driver_manages_iommu))
>
> Hmm, this code usually runs at enumeration time when no driver is
> attached to the device. Actually it would be pretty dangerous when this
> code runs while a driver is attached to the device. How does that change
> make things work for you?
>

I was seeing this get called via the path driver_probe_device() ->
platform_dma_configure() -> of_dma_configure() -> of_iommu_configure()
-> iommu_probe_device() -> ...

The only cases I was seeing where dev->driver is NULL where a few
places that drivers call of_dma_configure() on their own sub-devices.
But maybe there are some other paths that I did not notice?

BR,
-R