linux-kernel - Re: [PATCH] dma: Add Keystone Packet DMA Engine driver

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Message-ID: <53287213.3060705@ti.com>
Date:	Tue, 18 Mar 2014 12:19:31 -0400
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Vinod Koul <vinod.koul@...el.com>
CC:	<dmaengine@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
	Sandeep Nair <sandeep_n@...com>,
	Russell King <linux@....linux.org.uk>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH] dma: Add Keystone Packet DMA Engine driver

On Tuesday 18 March 2014 11:24 AM, Vinod Koul wrote:
> On Mon, Mar 17, 2014 at 03:37:47PM -0400, Santosh Shilimkar wrote:
>>>> To simplify this bit more, you can think of this as DMA channels, flows
>>>> are allocated and DMA channels are enabled by DMA engine and they remains
>>>> enabled always as long as the channel in use. Enablling dma channel
>>>> actually don't start the DMA transfer but just sets up the connection/pipe
>>>> with peripheral and memory and vice a versa.
>>>>
>>>> All the descriptor management, triggering, sending completion interrupt or
>>>> hardware signal to DMAEngine all managed by centralised QMSS.
>>>>
>>>> Actual copy of data is still done by DMA hardware but its completely
>>>> transparent to software. DMAEngine hardware takes care of that in the
>>>> backyard.
>>> So you will use the dmaengine just for setting up the controller. Not for actual
>>> transfers. Those would be governed by the QMSS, right?
>>>
>> Correct.
>>  
>>> This means that someone expecting to use dmaengine API will get confused about
>>> this and doing part (alloc) thru dmaengine and rest (transfers) using some other
>>> API. This brings to me the design approach, does it really make sense creating
>>> dmaengine driver for this when we are not fully complying to the API
>>>
>> Thats fair. The rationale behind usage of DMEngine was that its the closest
>> available subsystem which can be leveraged for this hardware. We can
>> pretty much use all the standard DMAEngine device tree parsing as well as
>> the config API to setup DMAs. 
>>
>> I think you made your stand clear, just to confirm, you don't prefer this
>> driver to be a DMAEngine driver considering it doesn't fully complying to
>> the APIs. We could document the deviation of 'transfer' handling to avoid
>> any confusion.
> Yup, a user will just get confused as the driver doenst conform the dmaengine
> API. Unless someone comes up witha  strong argument on why it should be
> dmaengine driver and what befits we see form such a model, i would like a
> damengine driver to comply to standard API and usage.
> 
OK thanks !!

Regards,
Santosh
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