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

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Message-ID: <1317492674.1573.1849.camel@vkoul-udesk3>
Date:	Sat, 01 Oct 2011 23:41:14 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Barry Song <21cnbao@...il.com>,
	Jassi Brar <jaswinder.singh@...aro.org>
Cc:	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 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.

@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.

-- 
~Vinod

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