linux-kernel - Re: [PATCH v2] PL330: Add PL330 DMA controller driver

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Date:	Thu, 25 Mar 2010 16:12:46 -0700
From:	Dan Williams <dan.j.williams@...el.com>
To:	jassi brar <jassisinghbrar@...il.com>
Cc:	Linus Walleij <linus.ml.walleij@...il.com>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	"kyungmin.park@...sung.com" <kyungmin.park@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Ben Dooks <ben-linux@...ff.org>
Subject: Re: [PATCH v2] PL330: Add PL330 DMA controller driver

On Thu, Mar 25, 2010 at 3:27 PM, jassi brar <jassisinghbrar@...il.com> wrote:
> On Fri, Mar 26, 2010 at 12:13 AM, Dan Williams <dan.j.williams@...el.com> wrote:
>> jassi brar wrote:
>>>>
>>>> Perhaps Joonyoung can simply port over the stuff
>>>> you need to this driver if you show your code.
>>>
>>> Having worked on Samsung SoCs(with PL330 DMAC) based products, I would be
>>> _very_ surprised if any user found this implementation useful.
>>> Let alone testing, this implementation can't even explain usability
>>> for fast peripherals
>>> with shallow FIFOs. I didn't give feedback for this patch because I am
>>> not sure if this
>>> is the right way to go at all.
>>
>> This is the wrong attitude.  If it were not for a simple oversight
>> Joonyoung's driver would already be upstream for the past two kernel
>> releases.  So you need to work together to improve that driver to
>> incorporate what you need.
> Nothing wrong in attitude here.
> Giving feedback on the code only comes after one is convinced with the
> overall approach taken. The last time I raised the PL330 driver issue,
> most people were not enthusiastic with this drivers/dma/ approach.
> I wasn't active mainline discussions when the driver was originally
> submitted a few months ago.
> And now my replies are not very 'polite' because theres a lot going on
> in the background that people in public threads don't know about.

Thanks for clarifying.

>
>
>> It sounds like you just need to add an extension for the arch specific dma
>> api.
> I actually plan more than that.
> Apart from inefficient design, JoonYoung's driver has made some fatal
> assumptions
> about PL330, which will result in DMA aborts if used with SoCs that implement
> configuration of PL330 that is very different from Samsung SoCs'
> Of course, I address all such issues that I can think of, in my implementation.

Ok, I'll rely on acked-by's from the interested parties once your
driver is out as I do not have a vested interest in this hardware,
just the dmaengine framework issues.

--
Dan
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