[RFC PATCH 1/1] iommu/arm-smmu: Add support for multiple TBU child devices

ARM MMU-500 implements a TBU (uTLB) for each connected master
besides a single TCU which controls and manages the address
translations. Each of these TBUs can either be in the same
power domain as the master, or they can have a independent
power switch.
This design addresses the challenges to control TBU power.
Adding child devices for each TBUs present in the configuration
lets us control the power and clocks to TLBs having individual
power domains. The device link between master devices (such as,
display, and GPU) and TBU devices ensures that the master takes
care of powering the smmu as long as it's available.
When the master is not available, the TBUs are identified with
sid and powered on.

Signed-off-by: Vivek Gautam <redacted>
---

 - The idea behind this patch is to handle the distributed smmu
   architectures, similar to MMU-500.
 - Untested yet.
 - There are still few instances where the correct tbu device has
   to be referenced and thus powered on to handle TLB maintenance
   operations.

 .../devicetree/bindings/iommu/arm,smmu.txt         |  27 +++
 drivers/iommu/arm-smmu.c                           | 191 +++++++++++++++++++--
 2 files changed, 205 insertions(+), 13 deletions(-)

diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.txt b/Documentation/devicetree/bindings/iommu/arm,smmu.txt
index d97a6bc8e608..7cf67e75022e 100644
--- a/Documentation/devicetree/bindings/iommu/arm,smmu.txt
+++ b/Documentation/devicetree/bindings/iommu/arm,smmu.txt

@@ -98,6 +98,18 @@ conditions.
                   accessed before master gets enabled and linked to its
                   SMMU.
 
+- child nodes:    ARM MMU-500 implements a TBU (page table cache or TLB) for
+                  each connected master besides a single TCU that controls
+                  and manages the address translations.
+                  Each of the child nodes represents a TBU that is attached to
+                  the master. This child node will have following property:
+
+  - compatibe:       must be "arm,mmu-500-tbu" for TBU child nodes of arm,mmu-500
+                     smmu.
+  - stream-id-range: array representing the starting stream id and the number
+                     of supported stream-ids. This gives information about
+                     the range of stream-ids that are supported by this TBU.