linux-kernel - Re: [PATCH] spi/pxa2xx-pci: Enable DMA binding through device name

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Date:	Fri, 25 Jul 2014 13:45:47 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	linux-arm-kernel@...ts.infradead.org,
	Kweh Hock Leong <hock.leong.kweh@...el.com>,
	Eric Miao <eric.y.miao@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Chew Chiau Ee <chiau.ee.chew@...el.com>,
	Darren Hart <dvhart@...ux.intel.com>, chiauee85@...il.com,
	linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org
Subject: Re: [PATCH] spi/pxa2xx-pci: Enable DMA binding through device name

On Fri, 2014-07-25 at 12:19 +0200, Arnd Bergmann wrote:
> On Friday 25 July 2014 12:55:59 Mika Westerberg wrote:
> > On Fri, Jul 25, 2014 at 12:07:14PM +0300, Mika Westerberg wrote:
> > > On Fri, Jul 25, 2014 at 10:38:36AM +0200, Arnd Bergmann wrote:
> > > > On Friday 25 July 2014 11:22:49 Mika Westerberg wrote:

[]

> > Something like this?

Arnd, this dependency to certain DMA driver looks really bad.

If we go that way, can we split that part to [another] module and make
it dependent to DW_DMAC?

Or shall we introduce a dmaengine type field in the platform data and
dynamically choose proper filter-whatever-function to get the channel?

> > Hock Leong / Chiaue Ee, are you able to check if this works on your BYT
> > machines?

> What I think you got wrong here (by following my bad advice) is the master
> number. Looking at the code for dw_dma, I think src_master needs to be '1'
> for your driver.

On some SoCs we have up to 4 masters. It's blurry for me how the SPI
should choose those masters. Currently it works fine, but I suspect
there are [might be] performance issues.

What about AVR32 case? We have to fix drivers as well there.

> the dw_dma driver can be simplified a little by removing the special
> case for the request line setting.

Yes, this part I like.

-- 
Andy Shevchenko <andriy.shevchenko@...el.com>
Intel Finland Oy

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