# Re: \[PATCH v4 4/8\] of: property: Add fw\_devlink support for optional properties

- From: Rob Herring \<robh@kernel.org\>
- Date: 2021-02-10 01:03:47 
- List: linux-doc
- Page: https://ratatoskr.run/linux-doc/2021/02/6264960
- Thread: https://ratatoskr.run/linux-doc/2021/02/6260845/t.md

```text
On Fri, Feb 05, 2021 at 02:26:40PM -0800, Saravana Kannan wrote:
> Not all DT bindings are mandatory bindings. Add support for optional DT
> bindings and mark iommus, iommu-map, dmas as optional DT bindings.

I don't think we can say these are optional or not. It's got to be a 
driver decision somehow.

For example, if IOMMU is optional, what happens with this sequence:

driver probes without IOMMU
driver calls dma_map_?()
IOMMU driver probes
h/w accesses DMA buffer --> BOOM!
```