[PATCH v5] devicetree: Add generic IOMMU device tree bindings

-----Original Message-----
From: Hiroshi Doyu [mailto:hdoyu at nvidia.com]
Sent: Tuesday, August 19, 2014 4:33 PM
To: Sethi Varun-B16395; Will Deacon
Cc: Hiroshi Doyu; Thierry Reding; Stephen Warren; Arnd Bergmann; Mark
Rutland; devicetree at vger.kernel.org; Olof Johansson; iommu at lists.linux-
foundation.org; Rob Herring; linux-tegra at vger.kernel.org; linux-arm-
kernel at lists.infradead.org; Yoder Stuart-B08248
Subject: Re: [PATCH v5] devicetree: Add generic IOMMU device tree bindings


Varun Sethi [off-list ref] writes:

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Also, for dynamic stream ID allocation we would need to
represent the specific master register (to store the stream ID) in the

device tree.

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I assmue that the above means that iMX has such configuration
register to map steramID and a device dynamically.

We have per master registers for setting the stream ID on the
Layerscape platforms. My point was that we would need the iommu
master node to include a reference to the master id register.

master at 1 {
               /* device has master ID 42 in the IOMMU */
             iommus = <&{/iommu} 42>;
             master-id-reg = <phandle offset> };

In the above, for "iommus=" bindings, you wouldn't need to break
ARM,SMMU compatibility at all if you set "streamID" exactly as below.

  master at 1 {
                 /* device has master ID 42 in the IOMMU */
               iommus = <&{/iommu} 'any given streamID'>;
               master-id-reg = <phandle offset>
  };

And your SoC needs to register bus_notifier and ADD_DEVICE should
configure to map 'any given streamID' to a device via the above
register. This wouldn't need any modification from ARM,SMMU driver
and keep the iommus bindings as it is.

IOW, SoC only needs to register ADD_DEVICE in bus_notifier to map
StreamID to a device. This needs to be executed earlier than IOMMU
bus's ADD_DEVICE, though.

Is my understanding right?

I don't think that SOC specific code needs a bus notifier for setting
the stream ID. It can be done as a part of SOC specific
initialization. The device tree can be updated to reflect the correct
stream ID (SMMU driver can get the updated stream ID from device
tree).

That's possible.

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I was thinking more on the lines of updating the device stream id
while attaching a device to the domain.

I thought the same but this would break the ARM,SMMU /compatibility/ since
the 1st param of "iommus=" is always expected as "streamID".

If streamID can be assigned dynamically like PCIe, not like streamID statically
set in DT, how should we describe this dynmaic steramID shifting/assignment in
DT?

 Can you dynamically program the stream ID for the device? If yes, then you require a unique numberspace for allocating a streamID. I am not clear on the stream ID translation requirement.

-Varun