linux-kernel - Re: [PATCHv2] DMAEngine: Let dmac drivers to set chan

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Date:	Thu, 28 Jul 2011 23:55:45 +0530
From:	Jaswinder Singh <jaswinder.singh@...aro.org>
To:	"Williams, Dan J" <dan.j.williams@...el.com>
Cc:	Russell King <rmk@....linux.org.uk>,
	"Koul, Vinod" <vinod.koul@...el.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-kernel@...r.kernel.org, linus.walleij@...ricsson.com,
	per.friden@...ricsson.com, wei.zhang@...escale.com,
	ebony.zhu@...escale.com, iws@...o.caltech.edu,
	s.hauer@...gutronix.de, maciej.sosnowski@...el.com,
	saeed@...vell.com, shawn.guo@...escale.com, yur@...raft.com,
	agust@...x.de, iwamatsu.nobuhiro@...esas.com,
	per.forlin@...ricsson.com, jonas.aberg@...ricsson.com,
	anemo@....ocn.ne.jp
Subject: Re: [PATCHv2] DMAEngine: Let dmac drivers to set chan_id

On 28 July 2011 23:44, Williams, Dan J <dan.j.williams@...el.com> wrote:
> On Thu, Jul 28, 2011 at 10:54 AM, Jaswinder Singh
> <jaswinder.singh@...aro.org> wrote:
>> On 28 July 2011 02:07, Russell King <rmk@....linux.org.uk> wrote:
>>>
>>>> On a serious note, my proposal, and the reply, shows the possibility
>>>> of having :-
>>>> a) Client drivers that are truly platform agnostic -- no platform_data
>>>> poking for
>>>>       channel selection
>>>
>>> I really doubt that's even possible.  Take this setup:
>>
>> I don't want to suggest anything wrong just because I didn't understand
>> your h/w.
>> I hope you will be kind enough to help me better understand your setup,
>> so that I have a fair chance to present my proposal.
>
> I don't understand all the slave usage models but the proposal seems
> fragile.  It wants to encode a whole bunch of arch specific details
> into a 32-bit code, but it still seems to me that there will always be
> platform specific details that don't fit the code.  Especially when we
> are still striving to ensure common behavior across drivers.  It seems
> the first step should be getting a few instances of a client driver
> interfacing with multiple dma drivers (via platform specific
> machinery) and see if anything common falls out of those
> implementations that can be pulled into dmaengine.  The proposal seems
> to be addressing a problem that we don't yet have (several clients
> associating with multiple channels in disparate and un-maintainable
> ways).

Dan, did you get time to read https://lkml.org/lkml/2011/7/28/97 ?

And please try to pose a scenario(however extreme) that you think
can't be handled by the mechanism.
Let us either kill the proposal or start implementing it if it's good.
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