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

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Message-ID: <CAJe_Zhe1YK8tqWsiPVfW6qHepfu4gd38EPsJ4+q2JFTtN-KfEQ@mail.gmail.com>
Date:	Sun, 2 Oct 2011 00:15:25 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	Barry Song <21cnbao@...il.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 23:41, Vinod Koul <vinod.koul@...el.com> wrote:
> On Sat, 2011-10-01 at 11:05 +0800, Barry Song 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.
>>
>> 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.
>>
>> How could we have two macro names: SRC_MEM, DEST_MEM for mapping. or just add:
>> dma_map_single_src
>> dma_map_single_dst
> Direction is valid even if you are doing memory to memory transfer. IMO
> what we need to specify what type of transfer (memory or peripheral),
> perhaps a flag and use that along with dma_data_direction.
I think dma_data_direction should be moved into dmac drivers that decide
the value from _more_ complete transfer info i.e, xfer_direction
IOW let clients pass more precise info to the dmac drivers via xfer_direction.

> @Jassi, this is what kind of tweak I have in mind. And i do not agree
> current approach is bad and is it cleanly tell us type of transfer
> (memcpy or prep_sg) and direction with dma_data _direction.
Not sure how is that "updating" the dma_data_direction ?
Please clarify what you exactly propose.
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