Re: [RFC 1/6] dma: Add Synopsys eDMA IP core driver

[Vinod Koul <vkoul@kernel.org>]

HI Gustavo,

On 03-01-19, 12:55, Gustavo Pimentel wrote:
> On 03/01/2019 12:45, Vinod Koul wrote:
> > On 03-01-19, 09:53, Gustavo Pimentel wrote:
> >> I've a doubt now. As you know, for a DMA transfer you need the source and
> >> destination addresses, which in the limited can be swapped according to the
> >> direction MEM_TO_DEV/DEV_TO_MEM case.
> >>
> >> For the sake of simplicity, I'll just consider now the MEM_TO_DEV case, since
> >> the other case is similar but the source and destination address are swapped.
> >>
> >> In my code I can get some of the information that I need by using the
> >> sg_dma_address() in the scatter-gather list (which gives me the source address).
> >>
> >> The remaining information I got from here, using the direction to help me to
> >> select which address I'll use later on the DMA transfer, in this case the
> >> destination address.
> >>
> >> Since this is deprecated how should I proceed? How can I get that information?
> >> There is some similar function to sg_dma_address() that could give me the
> >> destination address?
> > 
> > So the direction field is deprecated but rest of the configuration comes
> > from from dma_slave_config. The user should set src_addr, dst_addr and
> > then based on direction passed in the .device_prep_dma_* call arguments
> > one can use one of these as peripheral address.
> 
> Ok, and the address given by sg_dma_address()? Is redundant or not applicable
> for this case?

It is, it is the memory address you need to program. The device address
comes from dma_slave_config.

To elaborate, if you have MEM_TO_DEV use sg_dma_address() for src
address and dst_addr from dma_slave_config.

Similarly for DEV_TO_MEM, we use src_addr from dma_slave_config and
sg_dma_address()

The peripheral is static but memory buffer keeps changing wrt different
descriptors, so device address can be programmed once for multiple
descriptors to be transferred from a device.

HTH
-- 
~Vinod