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

Varun Sethi
2014-08-19T09:52:30Z

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 <Varun.Sethi@freescale.com> writes:
>
> >> -----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 <thierry.reding@gmail.com> writes:
> >>
> >> > +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.
>
> > 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