# Re: \[RFC PATCH v3 5/6\] dt-bindings: of: Add restricted DMA pool

- From: Florian Fainelli \<f.fainelli@gmail.com\>
- Date: 2021-01-07 18:16:05 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2021/01/6226979
- Thread: https://ratatoskr.run/linux-devicetree/2021/01/6224988/t.md

```text
On 1/7/21 10:00 AM, Konrad Rzeszutek Wilk wrote:
>>>
>>>
>>>  - Nothing stops the physical device from bypassing the SWIOTLB buffer.
>>>    That is if an errant device screwed up the length or DMA address, the
>>>    SWIOTLB would gladly do what the device told it do?
>>
>> So the system needs to provide a way to lock down the memory access, e.g. MPU.
> 
> OK! Would it be prudent to have this in the description above perhaps?

Yes this is something that must be documented as a requirement for the
restricted DMA pool users, otherwise attempting to do restricted DMA
pool is no different than say, using a device private CMA region.
Without the enforcement, this is just a best effort.
-- 
Florian
```