Hi Hiroshi,

-----Original Message-----
From: Hiroshi Doyu [mailto:hdoyu at nvidia.com]
Sent: Thursday, August 14, 2014 9:35 PM
To: Sethi Varun-B16395
Cc: Hiroshi Doyu; Thierry Reding; Stephen Warren; Arnd Bergmann; Will
Deacon; 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
Subject: Re: [PATCH v5] devicetree: Add generic IOMMU device tree bindings

Hi Varun,

Varun Sethi [off-list ref] writes:

quoted

quoted

-----Original Message-----
From: iommu-bounces at lists.linux-foundation.org [mailto:iommu-
bounces at lists.linux-foundation.org] On Behalf Of Hiroshi Doyu
Sent: Thursday, August 14, 2014 12:18 PM
To: Thierry Reding; Stephen Warren; Arnd Bergmann; Will Deacon
Cc: 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
Subject: Re: [PATCH v5] devicetree: Add generic IOMMU device tree
bindings


Thierry Reding [off-list ref] writes:

quoted

+Multiple-master IOMMU:
+----------------------
+
+       iommu {
+               /* the specifier represents the ID of the master */
+               #iommu-cells = <1>;
+       };
+
+       master at 1 {
+               /* device has master ID 42 in the IOMMU */
+               iommus = <&{/iommu} 42>;
+       };
+
+       master at 2 {
+               /* device has master IDs 23 and 24 in the IOMMU */
+               iommus = <&{/iommu} 23>, <&{/iommu} 24>;
+       };

I think that this "master ID" will be parsed in IOMMU driver. For
example, ARM,SMMU expects "streamID" as "master ID", right?

If a SoC has a feature to configure to assign streamID to devices at
runtime, "streamID" is not equal to "master ID".

  iommus = <&{/smmu} "soc specific master ID">;

"soc master ID" needs to be translated into "streamID" by SoC SW. It
seems that ARM,SMMU kernel driver doesn't expect this kind of ID
translation. If ARM,SMMU kernel driver is used as is, "soc master ID"
would be incompatible? ARM,SMMU needs such translation before
parsing. Is this my understanding right?

If so I think that this master ID configuration/translation may be
quite reasonable requirment for SoC using ARM,SMMU.

Can we consider this ID translation within ARM,SMMU compatibility?

IOW, is it possible to implement some SoC specific hook for ID
translation/configuration in ARM,SMMU kernel driver?

Can the id translation be done using a SMR mask?

No, "SoC master ID" is completely independenf of SMR.

quoted

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

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>
};

-Varun