Subject: What is the significance of coherent_dma_mask?

From: Venu Byravarasu <[email-masked]>
Date: Wed, 8 Aug 2012 09:28:17 +0530

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