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

[Vipin Kumar <vipin.kumar@st.com>]

On 10/10/2012 10:37 PM, Linus Walleij wrote:
> On Tue, Oct 9, 2012 at 12:44 PM, Vipin Kumar<vipin.kumar@st.com>  wrote:
>
>> read_buf/write_buf callbacks should be able to accept a user space memory
>> address (virtually contiguous memory) as buffer pointer.
>>
>> This patch allocates a logically contiguous memory area which is use for dma
>
> You mean PHYSICALLY contigous, don't you?
>

Yes Sorry for that :)

>> xfers during read and write accesses.
>>
>> Signed-off-by: Vipin Kumar<vipin.kumar@st.com>
>
> If you really want a physically contigous buffer you need to use
> CMA, but I don't think that is the real problem here...
>
> We're already using userspace buffers in e.g. the MMCI driver
> (drivers/mmc/host/mmci.c).
>
> The real problem is likely the DMA driver. The stuf that get
> fed into dma.device_prep_dma_memcpy() needs to be
> converted to a scatterlist and then set up in the LLI list
> for the controller.
>
> IIRC SPEAr is using drivers/dma/dw_dmac.c so
> check this driver's dwc_prep_dma_memcpy().
> It does seem like it is checking whether src or
> dest is scattered in this for() loop:
>
> for (offset = 0; offset<  len; offset += xfer_count<<  src_width) {}
>
> dma_sync_single_for_device() is translating the virtual
> address to physical for every chunk BTW.
>
> So instead of doing this copying, debug the problem, and
> see if there is a bug in that for()-loop or similar, if it needs
> to be rewritten or so.
>

I would debug again and reply to this mail soon

> Yours,
> Linus Walleij
> .
>