Re: [Xen-devel] [PATCH v7 8/8] xen/arm: add xen,dmabuf nodes

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 11/08/18 01:00, Stefano Stabellini wrote:
> Add a "xen-dmabuf" device node for every shared region, compatible
> "xen,dmabuf". Each of these nodes refers to the corresponding
> reserved-memory node using a phandle.
>
> These device nodes can be used to bind drivers that export the region to
> userspace, or do other operations based on the reserved memory region.
Nacked-by: Julien Grall <julien.grall@xxxxxxx>

As we discussed in a call few weeks ago, I am still against this.

The user is free to decide what to do with the reserved region. It could 
be bound to xen,dma-buf driver or any other driver.
Here what matters is to expose the sshm with useful information to 
distinguish between 2 of them.
Going forward, we should find a way for the user to describe which 
compatible should be used. This probably should go through the partial 
device-tree. One way to do this is:
1) Partial DT

mydriver@0xdeadbeef{
   xen-sshm = "ID"
}

2) The toolstack parse the partial DT and replace xen-sshm by the 
correct phandle
This means the xen-sshm property is never exposed, only the phandle. So 
this follow what Linux is doing. At the same time, you give freedom to 
the user to write its own driver baked by shared memory.
Cheers,

--
Julien Grall

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