Data corruption during direct-IO

[이재준 <jj76.lee@samsung.com>]

Hi everyone.

I'm working on some application which is using directly block device with
direct-IO.
When the application writes some patterns and reads it again. The pattern
is broken with 32bytes. I think that is due to the data-cache coherent
problem.

So, I inserted the code dma_cache_inv() before direct-IO().

After the patch, it works well. 

Could you tell me why the data is broken and why mips-kernel doesn't handle
data cache?

Thanks for any comments. 

Best Regards
JJ