[PATCH v7 5/7] arm64: Add support for FEAT_{LS64, LS64_V}

[Arnd Bergmann]

On Fri, Nov 14, 2025, at 10:25, Zhou Wang wrote:
> On 2025/11/14 0:26, Arnd Bergmann wrote:
>> 
>> Are you using a particular device, or are you trying to enable
>> the support in general? If you have a specific device you are
>> working on, does it use the PASID data or not?
>
> Many thanks for your careful explanation! I got the pointer here.
>
> We have a real device in our SoC, which supports LS64B/ST64B/ST64BV.
> For ST64BV, Our device just receives 64B data atomically, not interpret
> it with PASID data.

Ok, I see. So I assume this is either a kind of dedicated work queue
where the IOMMU PASID is set up in advance for the user MMIO area,
or it is a device that does not do any DMA at all, correct?

In this case, would the device also work correctly with ST64BV0 if
the ACCDATA register is fixed to a value of zero and you can only
use the upper 480 bits? Would it also work if there is an
unpredictable value in ACCDATA that may match the PASID of another
device used by the same process?

         Arnd