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

[Vivek Gautam]

Hi Rob,


On 09/19/2017 07:40 PM, Rob Herring wrote:

Thanks for reviewing the patch.

> On Tue, Sep 12, 2017 at 05:31:07PM +0530, Vivek Gautam wrote:
> > 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 <vivek.gautam@xxxxxxxxxxxxxx>
> > ---
> >
> >   - 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.
> Needs a vendor prefix.

Sure will add the vendor prefix.
This can be a generic arm-mmu500 implementation where,
a range of stream-ids are serviced by a TBU.
Would "arm,stream-id-range" make sense?

> Also need to document reg property. What does reg represent? If just an
> index with no correlation to h/w numbering, then perhaps stream ids
> could be put into reg instead.

Okay. Stream-ids make sense, since the reg doesn't necessarily represent
any hardware number such as channel number, etc.

Best regards
Vivek

> Rob
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