Re: [PATCH v7 3/3] iommu/tegra-smmu: Add PCI support

[Robin Murphy]

On 2020-10-15 05:13, Nicolin Chen wrote:
> On Wed, Oct 14, 2020 at 06:42:36PM +0100, Robin Murphy wrote:
> > On 2020-10-09 17:19, Nicolin Chen wrote:
> > > This patch simply adds support for PCI devices.
> > >
> > > Reviewed-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > > Tested-by: Dmitry Osipenko <digetx@xxxxxxxxx>
> > > Signed-off-by: Nicolin Chen <nicoleotsuka@xxxxxxxxx>
> > > ---
> > >
> > > Changelog
> > > v6->v7
> > >    * Renamed goto labels, suggested by Thierry.
> > > v5->v6
> > >    * Added Dmitry's Reviewed-by and Tested-by.
> > > v4->v5
> > >    * Added Dmitry's Reviewed-by
> > > v3->v4
> > >    * Dropped !iommu_present() check
> > >    * Added CONFIG_PCI check in the exit path
> > > v2->v3
> > >    * Replaced ternary conditional operator with if-else in .device_group()
> > >    * Dropped change in tegra_smmu_remove()
> > > v1->v2
> > >    * Added error-out labels in tegra_smmu_probe()
> > >    * Dropped pci_request_acs() since IOMMU core would call it.
> > >
> > >    drivers/iommu/tegra-smmu.c | 35 +++++++++++++++++++++++++----------
> > >    1 file changed, 25 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
> > > index be29f5977145..2941d6459076 100644
> > > --- a/drivers/iommu/tegra-smmu.c
> > > +++ b/drivers/iommu/tegra-smmu.c
> > > @@ -10,6 +10,7 @@
> > >    #include <linux/kernel.h>
> > >    #include <linux/of.h>
> > >    #include <linux/of_device.h>
> > > +#include <linux/pci.h>
> > >    #include <linux/platform_device.h>
> > >    #include <linux/slab.h>
> > >    #include <linux/spinlock.h>
> > > @@ -865,7 +866,11 @@ static struct iommu_group *tegra_smmu_device_group(struct device *dev)
> > >    	group->smmu = smmu;
> > >    	group->soc = soc;
> > > -	group->group = iommu_group_alloc();
> > > +	if (dev_is_pci(dev))
> > > +		group->group = pci_device_group(dev);
> >
> > Just to check, is it OK to have two or more swgroups "owning" the same
> > iommu_group if an existing one gets returned here? It looks like that might
> > not play nice with the use of iommu_group_set_iommudata().
>
> Do you mean by "gets returned here" the "IS_ERR" check below?

I mean that unlike iommu_group_alloc()/generic_device_group(), 
pci_device_group() may give you back a group that already contains 
another device and has already been set up from that device's 
perspective. This can happen for topological reasons like requester ID 
aliasing through a PCI-PCIe bridge or lack of isolation between functions.

Robin.

> > > +	else
> > > +		group->group = generic_device_group(dev);
> > > +
> > >    	if (IS_ERR(group->group)) {
> > >    		devm_kfree(smmu->dev, group);
> > >    		mutex_unlock(&smmu->lock);