linux-kernel - Re: [PATCHv4] DMAEngine: Define interleaved transfer request api

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Date:	Sun, 2 Oct 2011 00:11:08 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Barry Song <21cnbao@...il.com>
Cc:	Vinod Koul <vinod.koul@...el.com>, linux-kernel@...r.kernel.org,
	dan.j.williams@...el.com, rmk@....linux.org.uk,
	DL-SHA-WorkGroupLinux <workgroup.linux@....com>
Subject: Re: [PATCHv4] DMAEngine: Define interleaved transfer request api

On 1 October 2011 08:35, Barry Song <21cnbao@...il.com> wrote:
> 2011/10/1 Jassi Brar <jaswinder.singh@...aro.org>:
>> On 30 September 2011 12:13, Barry Song <21cnbao@...il.com> wrote:
>>>
>>> i support we can update dma_data_direction to:   MEM_TO_MEM,
>>> MEM_TO_DEV,  DEV_TO_MEM, DEV_TO_DEV.
>>>
>> So basically you are suggesting to replace 'enum dma_data_direction'
>> with 'enum xfer_direction'
>> I am not sure about that. I think they represent different things and
>> hence should be separate.
>> dma_data_direction tells the mapping of a buffer while the other
>> tells if the src and dst are memory or a device's FIFO.
>>
> you are kind of right now. now people use dma_data_direction to do
> mapping for dma buffer. even with all 4 direction, people still use
> the old two direction to do mapping.
> For example, it can't use
> MEM_TO_MEM to map, it still need to know whether the memory is source
> or dest.
MEM_TO_MEM means "From Memory Source To Memory Destination"
  Map Src buffer with DMA_TO_DEVICE and Dst buffer with DMA_FROM_DEVICE

MEM_TO_DEV means "From Memory Source To FIFO Destination"
  Map Src buffer with DMA_TO_DEVICE.

DEV_TO_MEM means "From FIFO Source To Memory Destination"
  Map Dst buffer with DMA_FROM_DEVICE

DEV_TO_DEV means "From FIFO Source To FIFO Destination"

What else would you want to know ?

> i just don't like to the two old macro names. it seems i get a ticket
> flying from New York to Beijing, but actually, we fly to Mexico...
> so by the moment, dma_data_direction seems just to mean how to do map,
> but xfer_direction is the real transfer direction.
Not every dmac driver would need to know the src and dst type _only_ for buffer
mapping. Some might have to reprogram the channel accordingly, say.
The point is to give exact info about src and dst to dmac client driver and let
it do what it must.

> How could we have two macro names: SRC_MEM, DEST_MEM for mapping. or just add:
> dma_map_single_src
> dma_map_single_dst
Not sure what you mean by this.
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