linux-kernel - Re: [RFC/PATCHv2 3/3] driver: spi: Add quad spi read support

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Date:	Thu, 18 Jul 2013 17:22:01 +0530
From:	Sourav Poddar <sourav.poddar@...com>
To:	Mark Brown <broonie@...nel.org>
CC:	<spi-devel-general@...ts.sourceforge.net>,
	<grant.likely@...aro.org>, <balbi@...com>, <rnayak@...com>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC/PATCHv2 3/3] driver: spi: Add quad spi read support

On Thursday 18 July 2013 04:14 PM, Mark Brown wrote:
> On Thu, Jul 18, 2013 at 03:31:27PM +0530, Sourav Poddar wrote:
>> Since, qspi controller uses quad read.
>>
>> Configuring the command register, if the transfer of data needs
>> dual or quad lines.
>>
>> This patch has been done on top of the following patch[1], which is just the
>> basic idea of adding dual/quad support in spi framework.
>> $subject patch will undergo changes as the parent patch goes[1]
>>
>> [1]: http://comments.gmane.org/gmane.linux.kernel.spi.devel/14047
> Just as with commit IDs you should include a plain text description of
> anything you link to so that people reading your e-mail can tell what
> you're talking about without going on line.
Ok, will keep that in mind for future.

Just to give you a brief description here,
Requirement is to have a dual/quad support in spi frameowrk, so that
drivers can use multiple lines for data transfers.

What patch[1] tries to does, is
[1]:  http://comments.gmane.org/gmane.linux.kernel.spi.devel/14047

is to add to each transfer the bitwidth it supports, so that that 
bitwidth information
can be parsed in controller driver and can be used for respective 
read/writes.

A typical usecase on my side is,
I have a spansion flash connected to qspi. Flash device supports quad 
read with
a certain read opcode(QUAD_READ). So, Whenever the opcode send is QUAD_READ,
we will append that information as a bitwidth to the spi transfer. This 
information will
be parsed by the controller driver and will be used to configure the cmd 
reg to do
the particular type of reads.
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