[PATCH 07/11] fsmc/nand: Provide contiguous buffers to dma

[Linus Walleij]

On Thu, Oct 11, 2012 at 6:15 AM, viresh kumar <viresh.kumar at linaro.org> wrote:
> On Wed, Oct 10, 2012 at 10:37 PM, Linus Walleij
> <linus.walleij at linaro.org> wrote:

>> dma_sync_single_for_device() is translating the virtual
>> address to physical for every chunk BTW.
>
> I pray that i am wrong here, otherwise i would be thrown out from
> the maintainers list for this driver :)
>
> dma_sync_single_for_device() is not doing anything on the buffer, but
> on the LLI item. Actually it is flushing LLI struct so that DMA h/w can get
> the correct values.

Sorry no, I'm the one who's wrong...

So the DMA engine memcpy() is not mapping virt->phys
but expects physical addresses to be provided.

So dma_map_single() needs to be called on the stuff
passed in to dev->device_prep_dma_memcpy().

And currently there is indeed a dma_map_single() in
dma_xfer() in fsmc_nand.c which should work just fine.

dma_map_single() will only work if the buffer is
physically contiguous.

And the block layer of the subsystem should take care
of only handing the driver buffers that are contiguous
I think? Not that I'm an expert here ... more some
guesswork :-/

Artem will know I hope!

Yours,
Linus Walleij