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

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Date:	Fri, 30 Sep 2011 21:17:07 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	linux-kernel@...r.kernel.org, dan.j.williams@...el.com,
	rmk@....linux.org.uk, 21cnbao@...il.com
Subject: Re: [PATCHv4] DMAEngine: Define interleaved transfer request api

On 29 September 2011 16:47, Vinod Koul <vinod.koul@...el.com> wrote:
> On Wed, 2011-09-28 at 20:45 +0530, Jassi Brar wrote:
>> >> +enum xfer_direction {
>> >> +     MEM_TO_MEM,
>> >> +     MEM_TO_DEV,
>> >> +     DEV_TO_MEM,
>> >> +     DEV_TO_DEV,
>> > Use/update dma_data_direction.
>> dma_data_direction is the mapping attribute of a buffer.
>> While that info is what some dmac driver might need ultimately, our
>> main aim here is to tell exactly if Src and Dst is Memory or a
>> device's FIFO.
>>
>> Mapping attribute of src/dst buffers could be very well deducted from
>> xfer_direction, but dma_data_direction isn't meant to tell if Src and
>> Dst is Mem or FIFO.
>> Also, for (SLAVE && !src_inc && !dst_inc) we need to disambiguate
>> three options  Mem->Fifo,  Fifo->Mem,  *Fifo->Fifo*(not impossible)
>> So while using dma_data_direction would work today, that sure is hacky
>> and not future-proof.
> That is why I said use/update, you missed the update part.
>
> One way would be to use direction field with new flag indicating if its
> memory or device transfer, otherwise you can expand this enum.
>
> Point is few things are already there so improve upon it rather than
> have two structures in kernel doing similar things...
>
I don't think dma_data_direction should be messed with here.
Or I am just being ignorant, in that case please do suggest how do
you want dma_data_direction "updated" ?
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