Enabling D-cache for OneNAND bufferram

[Joakim Tjernlund]

>
> Hello!
>
> I am currently writing a piece of software that takes advantage of the
> fact that OneNAND supports read-while-loading. What I am doing is trying
> to achieve higher efficiency when decoding data from the OneNAND by
> decoding data that is available in the OneNAND bufferram directly
> instead of copying it to normal RAM and decoding there. So far, I have
> gotten quite poor results due to the fact that the bufferrams are not
> cached (for good reason since it is Device memory). My software will be
> used on ARM devices of different types, with my testrigs being a Nokia
> N810 and a N900.
>
> I have exclusive access to the OneNAND chip, and as such know exactly
> what information is stored in the bufferrams at all times. If I could
> only enable the D-cache for the bufferrams, I could therefore make sure
> to invalidate the cache whenever I reprogram the OneNAND chip.
>
>  From what I have read so far, it seems that the only way to enable
> cacheing of the bufferrams would be to somehow change how the memory
> attributes for the memory region in the MMU. I have however not found
> any easy way of doing this. Any tips? I dont really have very much
> experience when it comes to how the MMU works.

Have a look at ioremap_cached(). Seems to be availabe on ARM
Basically you need to create a second virtual address mapping of the devices
RAM which is cached.

    Jocke