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

[Hiroshi Doyu <hdoyu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>]

Varun Sethi <Varun.Sethi-KZfg59tc24xl57MIdRCFDg@public.gmane.org> writes:

>> >> > 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@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@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.

> 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?