The bus_set_iommu() in tegra_smmu_probe() enumerates all clients
to call in tegra_smmu_probe_device() where each client searches
its DT node for smmu pointer and swgroup ID, so as to configure
an fwspec. But this requires a valid smmu pointer even before mc
and smmu drivers are probed. So in tegra_smmu_probe() we added a
line of code to fill mc->smmu, marking "a bit of a hack".

This works for most of clients in the DTB, however, doesn't work
for a client that doesn't exist in DTB, a PCI device for example.

Actually, if we return ERR_PTR(-ENODEV) in ->probe_device() when
it's called from bus_set_iommu(), iommu core will let everything
carry on. Then when a client gets probed, of_iommu_configure() in
iommu core will search DTB for swgroup ID and call ->of_xlate()
to prepare an fwspec, similar to tegra_smmu_probe_device() and
tegra_smmu_configure(). Then it'll call tegra_smmu_probe_device()
again, and this time we shall return smmu->iommu pointer properly.

So we can get rid of tegra_smmu_find() and tegra_smmu_configure()
along with DT polling code by letting the iommu core handle every
thing, except a problem that we search iommus property in DTB not
only for swgroup ID but also for mc node to get mc->smmu pointer
to call dev_iommu_priv_set() and return the smmu->iommu pointer.
So we'll need to find another way to get smmu pointer.

Referencing the implementation of sun50i-iommu driver, of_xlate()
has client's dev pointer, mc node and swgroup ID. This means that
we can call dev_iommu_priv_set() in of_xlate() instead, so we can
simply get smmu pointer in ->probe_device().

This patch reworks tegra_smmu_probe_device() by:
1) Removing mc->smmu hack in tegra_smmu_probe() so as to return
   ERR_PTR(-ENODEV) in tegra_smmu_probe_device() during stage of
   tegra_smmu_probe/tegra_mc_probe().
2) Moving dev_iommu_priv_set() to of_xlate() so we can get smmu
   pointer in tegra_smmu_probe_device() to replace DTB polling.
3) Removing tegra_smmu_configure() accordingly since iommu core
   takes care of it.

This also fixes a problem that previously we could add clients to
iommu groups before iommu core initializes its default domain:
    ubuntu@jetson:~$ dmesg | grep iommu
    platform 50000000.host1x: Adding to iommu group 1
    platform 57000000.gpu: Adding to iommu group 2
    iommu: Default domain type: Translated
    platform 54200000.dc: Adding to iommu group 3
    platform 54240000.dc: Adding to iommu group 3
    platform 54340000.vic: Adding to iommu group 4

Though it works fine with IOMMU_DOMAIN_UNMANAGED, but will have
warnings if switching to IOMMU_DOMAIN_DMA:
    iommu: Failed to allocate default IOMMU domain of type 0 for
           group (null) - Falling back to IOMMU_DOMAIN_DMA
    iommu: Failed to allocate default IOMMU domain of type 0 for
           group (null) - Falling back to IOMMU_DOMAIN_DMA

Now, bypassing the first probe_device() call from bus_set_iommu()
fixes the sequence:
    ubuntu@jetson:~$ dmesg | grep iommu
    iommu: Default domain type: Translated
    tegra-host1x 50000000.host1x: Adding to iommu group 0
    tegra-dc 54200000.dc: Adding to iommu group 1
    tegra-dc 54240000.dc: Adding to iommu group 1
    tegra-vic 54340000.vic: Adding to iommu group 2
    nouveau 57000000.gpu: Adding to iommu group 3

Note that dmesg log above is testing with IOMMU_DOMAIN_UNMANAGED.
Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
Tested-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20201125101013.14953-5-nicoleotsuka@gmail.comSigned-off-by: Will Deacon <will@kernel.org>