Re: [PATCH 2/5] iommu/arm-smmu: add support for PCI master devices

[Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>]

On Wed, Jul 09, 2014 at 03:13:04PM +0100, Alex Williamson wrote:
> On Wed, 2014-07-09 at 14:26 +0100, Will Deacon wrote:
> > [Adding Alex; question below]
> > 
> > On Thu, Jul 03, 2014 at 03:22:37PM +0100, Varun Sethi wrote:
> > > > +static int __arm_smmu_get_pci_sid(struct pci_dev *pdev, u16 alias, void
> > > > +*data) {
> > > > +     *((u16 *)data) = alias;
> > > > +     return 0; /* Continue walking */
> > > > +}
> > 
> > [...]
> > 
> > > > @@ -1598,15 +1642,36 @@ static int arm_smmu_add_device(struct device
> > > > *dev)
> > > >               return PTR_ERR(group);
> > > >       }
> > > >
> > > > +     if (dev_is_pci(dev)) {
> > > > +             struct arm_smmu_master_cfg *cfg;
> > > > +             struct pci_dev *pdev = to_pci_dev(dev);
> > > > +
> > > > +             cfg = kzalloc(sizeof(*cfg), GFP_KERNEL);
> > > > +             if (!cfg) {
> > > > +                     ret = -ENOMEM;
> > > > +                     goto out_put_group;
> > > > +             }
> > > > +
> > > > +             cfg->num_streamids = 1;
> > > > +             pci_for_each_dma_alias(pdev, __arm_smmu_get_pci_sid,
> > > > +                                    &cfg->streamids[0]);
> > > [Sethi Varun-B16395] We need to look for upstream DMA device. We should be
> > > using pci_find_dma_isolation_root here. Also, this would also imply that
> > > there could be multiple devices sharing the same stream ID. So, we should
> > > check if a particular stream ID value has already been configured in the
> > > SMR registers.
> > 
> > pci_find_dma_isolation_root doesn't exist in any of the trees I have. Alex,
> > is this queued anywhere and do I actually need it?
> 
> That function was in the v3 DMA alias series, in v4 it got replaced.
> iommu_group_get_for_pci_dev() is the common function for finding or
> creating a group for a device and pci_for_each_dma_alias() is the
> interface to walk each alias in a PCI topology.  The pci_ interface is
> in 3.16-rc and the iommu_ pieces are current in next via the iommu tree.

Cheers, Alex. I'll move my driver to using iommu_group_get_for_pci_dev once
that's hit mainline (since I currently put each master into its own group).

> > The purpose of this code is to find the requester ID of a device as it
> > appears at the host controller. At this point, we can map it (via firmware
> > tables that are TBD) to a Stream ID for the SMMU. It looks to me like
> > pci_for_each_dma_alias walks over non-transparent PCI bridges correctly, so
> > the callback I provide just updates the alias until the walk has completed.
> 
> Yep, that's the intended usage.  There are cases in VT-d where it wants
> to add context entries for every alias and cases elsewhere that we just
> want the final alias.  pci_for_each_dma_alias() is meant to fit both use
> cases.  Thanks,

Cracking, cheers for confirming.

Will