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Date: Fri, 18 Oct 2013 11:40:15 +0530
From: Sourav Poddar <sourav.poddar@ti.com>
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To: Trent Piepho <tpiepho@gmail.com>
Subject: Re: [PATCH 1/3] spi/qspi: Add memory mapped read support.
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Cc: Peter Korsgaard <peter@korsgaard.com>, "Balbi, Felipe" <balbi@ti.com>,
 Mark Brown <broonie@kernel.org>,
 "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>, "Gupta,
 Pekon" <pekon@ti.com>, "spi-devel-general@lists.sourceforge.net"
 <spi-devel-general@lists.sourceforge.net>,
 Brian Norris <computersforpeace@gmail.com>,
 David Woodhouse <dwmw2@infradead.org>
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On Friday 18 October 2013 11:26 AM, Trent Piepho wrote:
> On Thu, Oct 17, 2013 at 9:06 PM, Sourav Poddar<sourav.poddar@ti.com>  wrote:
>> On Friday 18 October 2013 05:12 AM, Mark Brown wrote:
>>>> Are you looking for comparison between  read_via_dma() v/s memcpy() ?
>>> No, I'm looking for a comparison of normal SPI mode (which I'd have
>>> expected to DMA) and the memcpy() mode.
>>>
>>>> If yes, then unfortunately we are bit constrained because our controller
>>>> does not support DMA. So, we have to depend on CPU based memcpy()
>>>> only. However, use of DMA can be added as an independent patch on
>>>> top of this CASE-2 patch.
>>> However if the controller can't DMA at all then that's not going to be
>>> possible...  am I understanding you correctly that normal SPI can't DMA?
>> Yes, you are correct, the normal SPI cant DMA.
> Hardware limitation or driver limitation?  Adding DMA support to the
> driver might be much more useful than adding memory mapped read
> support.
Its a hardware limitation, the qspi controller does not support DMA.