powerpc/iommu: Reimplement the iommu_table_group_ops for pSeries

PPC64 IOMMU API defines iommu_table_group_ops which handles DMA
windows for PEs, their ownership transfer, create/set/unset the TCE
tables for the Dynamic DMA wundows(DDW). VFIOS uses these APIs for
support on POWER.

The commit 9d67c943 ("powerpc/iommu: Add "borrowing"
iommu_table_group_ops") implemented partial support for this API with
"borrow" mechanism wherein the DMA windows if created already by the
host driver, they would be available for VFIO to use. Also, it didn't
have the support to control/modify the window size or the IO page
size.

The current patch implements all the necessary iommu_table_group_ops
APIs there by avoiding the "borrrowing". So, just the way it is on the
PowerNV platform, with this patch the iommu table group ownership is
transferred to the VFIO PPC subdriver, the iommu table, DMA windows
creation/deletion all driven through the APIs.

The pSeries uses the query-pe-dma-window, create-pe-dma-window and
reset-pe-dma-window RTAS calls for DMA window creation, deletion and
reset to defaul. The RTAs calls do show some minor differences to the
way things are to be handled on the pSeries which are listed below.

* On pSeries, the default DMA window size is "fixed" cannot be custom
sized as requested by the user. For non-SRIOV VFs, It is fixed at 2GB
and for SRIOV VFs, its variable sized based on the capacity assigned
to it during the VF assignment to the LPAR. So, for the  default DMA
window alone the size if requested less than tce32_size, the smaller
size is enforced using the iommu table->it_size.

* The DMA start address for 32-bit window is 0, and for the 64-bit
window in case of PowerNV is hardcoded to TVE select (bit 59) at 512PiB
offset. This address is returned at the time of create_table() API call
(even before the window is created), the subsequent set_window() call
actually opens the DMA window. On pSeries, the DMA start address for
32-bit window is known from the 'ibm,dma-window' DT property. However,
the 64-bit window start address is not known until the create-pe-dma
RTAS call is made. So, the create_table() which returns the DMA window
start address actually opens the DMA window and returns the DMA start
address as returned by the Hypervisor for the create-pe-dma RTAS call.

* The reset-pe-dma RTAS call resets the DMA windows and restores the
default DMA window, however it does not clear the TCE table entries
if there are any. In case of ownership transfer from platform domain
which used direct mapping, the patch chooses remove-pe-dma instead of
reset-pe for the 64-bit window intentionally so that the
clear_dma_window() is called.

Other than the DMA window management changes mentioned above, the
patch also brings back the userspace view for the single level TCE
as it existed before commit 090bad39

 ("powerpc/powernv: Add
indirect levels to it_userspace") along with the relavent
refactoring.

Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/171923275958.1397.907964437142542242.stgit@linux.ibm.com