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

[Hiroshi Doyu]

Hi Varun,

Varun Sethi <Varun.Sethi at 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 at 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.