# What is the significance of coherent\_dma\_mask?

- From: Venu Byravarasu \<hidden\>
- Date: 2012-08-08 04:05:43 
- List: netdev
- Page: https://ratatoskr.run/netdev/2012/08/3905101
- Thread: https://ratatoskr.run/netdev/2012/08/3905101/t.md

```text
Hi,

Some of the USB drivers are setting coherent_dma_mask & many others are not doing it.
From the description present in the comment beside this field in device.h, I could not understand its real significance.

Can some one plz let me know its real need and use case where it is mandatory to use it?

Thanks,
Venu
```