linux-kernel - Re: [PATCH] iommu/exynos: add devices attached to the System MMU to an IOMMU group

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Message-ID: <CAG8rG2wNG9wVjKxtaDzLRybvh3wPVR08j9G9OPcK=a2Gwbtg-g@mail.gmail.com>
Date:	Tue, 23 Jul 2013 13:00:29 +0200
From:	Antonios Motakis <a.motakis@...tualopensystems.com>
To:	Inki Dae <inki.dae@...sung.com>
Cc:	Linux ARM Kernel <linux-arm-kernel@...ts.infradead.org>,
	Linux IOMMU <iommu@...ts.linux-foundation.org>,
	Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>,
	kvm-arm <kvmarm@...ts.cs.columbia.edu>,
	Cho KyongHo <pullip.cho@...sung.com>,
	Joerg Roedel <joro@...tes.org>,
	Sachin Kamat <sachin.kamat@...aro.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Wei Yongjun <yongjun_wei@...ndmicro.com.cn>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu/exynos: add devices attached to the System MMU to
 an IOMMU group

On Tue, Jul 23, 2013 at 12:31 PM, Inki Dae <inki.dae@...sung.com> wrote:
>
>
>
> > -----Original Message-----
> > From: linux-samsung-soc-owner@...r.kernel.org [mailto:linux-samsung-soc-
> > owner@...r.kernel.org] On Behalf Of Antonios Motakis
> > Sent: Tuesday, July 23, 2013 7:02 PM
> > To: linux-arm-kernel@...ts.infradead.org;
> iommu@...ts.linux-foundation.org;
> > linux-samsung-soc@...r.kernel.org
> > Cc: kvmarm@...ts.cs.columbia.edu; Antonios Motakis; Cho KyongHo; Joerg
> > Roedel; Sachin Kamat; Jiri Kosina; Wei Yongjun; open list
> > Subject: [PATCH] iommu/exynos: add devices attached to the System MMU to
> > an IOMMU group
> >
> > IOMMU groups are expected by certain users of the IOMMU API,
> > e.g. VFIO. Since each device is behind its own System MMU, we
> > can allocate a new IOMMU group for each device.
> >
> > This patch depends on Cho KyongHo's patch series titled "[PATCH v7 00/12]
> > iommu/exynos: Fixes and Enhancements of System MMU driver with DT",
> > applied on a Linux 3.10.1 kernel. It has been tested on the Arndale board.
> >
> > Signed-off-by: Antonios Motakis <a.motakis@...tualopensystems.com>
> > ---
> >  drivers/iommu/exynos-iommu.c | 24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> >
> > diff --git a/drivers/iommu/exynos-iommu.c b/drivers/iommu/exynos-iommu.c
> > index 51d43bb..9f39eaa 100644
> > --- a/drivers/iommu/exynos-iommu.c
> > +++ b/drivers/iommu/exynos-iommu.c
> > @@ -1134,6 +1134,28 @@ static phys_addr_t exynos_iommu_iova_to_phys(struct
> > iommu_domain *domain,
> >       return phys;
> >  }
> >
> > +static int exynos_iommu_add_device(struct device *dev)
> > +{
> > +     struct iommu_group *group;
> > +     int ret;
> > +
> > +     group = iommu_group_alloc();
>
> Is that correct? I don't see why you allocate a group object every time
> add_device callback is called. That doesn't have any meaning we have to use
> iommu group feature. I think the implementation should be one more devices
> per a group. So I guess a given device object should be wrapped by higher
> device object than the given device object. For a good example, you can
> refer to intel-iommu.c file.

With an Intel IOMMU it can be the case that 2 devices have to share
the same IOMMU mappings (i.e. you can't program them separately). With
the Exynos System MMU, there is always one System MMU per device, so
there is nothing stopping you from programming any 2 devices' mappings
differently. So yes, the right thing to do here is to have a one to
one relationship between devices and IOMMU groups.

(resending because of html mail)

Cheers,
Antonios

>
>
> Thanks,
> Inki Dae
>
> > +     if (IS_ERR(group)) {
> > +             dev_err(dev, "Failed to allocate IOMMU group\n");
> > +             return PTR_ERR(group);
> > +     }
> > +
> > +     ret = iommu_group_add_device(group, dev);
> > +     iommu_group_put(group);
> > +
> > +     return ret;
> > +}
> > +
> > +static void exynos_iommu_remove_device(struct device *dev)
> > +{
> > +     iommu_group_remove_device(dev);
> > +}
> > +
> >  static struct iommu_ops exynos_iommu_ops = {
> >       .domain_init = &exynos_iommu_domain_init,
> >       .domain_destroy = &exynos_iommu_domain_destroy,
> > @@ -1142,6 +1164,8 @@ static struct iommu_ops exynos_iommu_ops = {
> >       .map = &exynos_iommu_map,
> >       .unmap = &exynos_iommu_unmap,
> >       .iova_to_phys = &exynos_iommu_iova_to_phys,
> > +     .add_device     = exynos_iommu_add_device,
> > +     .remove_device  = exynos_iommu_remove_device,
> >       .pgsize_bitmap = SECT_SIZE | LPAGE_SIZE | SPAGE_SIZE,
> >  };
> >
> > --
> > 1.8.1.2
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-samsung-
> > soc" in
> > the body of a message to majordomo@...r.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
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