Re: [PATCH v5 0/4] vfio/dma-buf: add TPH support for peer-to-peer access

["Christian König" <christian.koenig@amd.com>]

On 5/29/26 08:34, Zhiping Zhang wrote:
...
> There's no in-tree vendor PF driver

Well I have to admit it's a bit on the edge but this sentence is a show stopper.

DMA-buf is an in kernel interface for buffer sharing between drivers and any change to it needs an in kernel driver as justification for the added complexity.

> — the device is a Meta MTIA
> accelerator managed entirely from userspace via VFIO passthrough.

When you have a complete open source driver stack which utilizes VFIO passthrough as the interface to communicate with the kernel drivers then we can eventually talk about that.

But as far as I can see without upstreaming or at least open sourcing the full stack to utilize this functionality it's a clear NAK to upstreaming this.

Regards,
Christian.


> That's why the ST has to flow through a uAPI: userspace owns the
> device and its ST table, so it's the only entity that can publish a
> meaningful value for a given dma-buf.
> 
> On the effect: the endpoint's PCIe ingress block uses the 8-bit ST as
> an in-band instruction for the incoming P2P TLP — selecting a target
> cache partition and, on writes, an in-flight operation on the data
> before it lands. The dma-buf callback keeps this opaque to the
> framework — only the producer (userspace owner of the VFIO device) and
> the consumer (endpoint block) need to interpret the value.
> 
> will include these words into v6's cover letter.
> 
> Thanks,
> Zhiping